diff --git a/lib/webrat/core/elements/field.rb b/lib/webrat/core/elements/field.rb
index 4d74f6e..815575b 100644
--- a/lib/webrat/core/elements/field.rb
+++ b/lib/webrat/core/elements/field.rb
@@ -1,6 +1,7 @@
 require "cgi"
+require "digest/md5"
 require "webrat/core_extensions/blank"
-require "webrat/core_extensions/nil_to_param"
+require "webrat/core_extensions/nil_to_query_string"
 
 require "webrat/core/elements/element"
 
@@ -13,7 +14,7 @@ module Webrat
     attr_reader :value
 
     def self.xpath_search
-      [".//button", ".//input", ".//textarea", ".//select"]
+      ".//button|.//input|.//textarea|.//select"
     end
 
     def self.xpath_search_excluding_hidden
@@ -84,19 +85,17 @@ module Webrat
       raise DisabledFieldError.new("Cannot interact with disabled form element (#{self})")
     end
 
-    def to_param
+    def to_query_string
       return nil if disabled?
 
-      params = case Webrat.configuration.mode
-      when :rails
-        parse_rails_request_params("#{name}=#{escaped_value}")
-      when :merb
-        ::Merb::Parse.query("#{name}=#{escaped_value}")
-      else
-        { name => [*@value].first.to_s }
+      query_string = case Webrat.configuration.mode
+      when :rails, :merb, :rack, :sinatra
+        build_query_string
+      when :mechanize
+        build_query_string(false)
       end
 
-      unescape_params(params)
+      query_string
     end
 
     def set(value)
@@ -109,18 +108,6 @@ module Webrat
 
   protected
 
-    def parse_rails_request_params(params)
-      if defined?(ActionController::AbstractRequest)
-        ActionController::AbstractRequest.parse_query_parameters(params)
-      elsif defined?(ActionController::UrlEncodedPairParser)
-        # For Rails > 2.2
-        ActionController::UrlEncodedPairParser.parse_query_parameters(params)
-      else
-        # For Rails > 2.3
-        Rack::Utils.parse_nested_query(params)
-      end
-    end
-
     def form
       Form.load(@session, form_element)
     end
@@ -138,23 +125,20 @@ module Webrat
       @element["name"]
     end
 
-    def escaped_value
-      CGI.escape(@value.to_s)
+    def build_query_string(escape_value=true)
+      if @value.is_a?(Array)
+        @value.collect {|value| "#{name}=#{ escape_value ? escape(value) : value }" }.join("&")
+      else
+        "#{name}=#{ escape_value ? escape(value) : value }"
+      end
     end
 
-    # Because we have to escape it before sending it to the above case statement,
-    # we have to make sure we unescape each value when it gets back so assertions
-    # involving characters like <, >, and &  work as expected
-    def unescape_params(params)
-      case params.class.name
-      when 'Hash', 'Mash'
-        params.each { |key,value| params[key] = unescape_params(value) }
-        params
-      when 'Array'
-        params.collect { |value| unescape_params(value) }
-      else
-        CGI.unescapeHTML(params)
-      end
+    def escape(value)
+      CGI.escape(value.to_s)
+    end
+
+    def escaped_value
+      CGI.escape(@value.to_s)
     end
 
     def labels
@@ -186,22 +170,6 @@ module Webrat
     def default_value
       @element["value"]
     end
-
-    def replace_param_value(params, oval, nval)
-      output = Hash.new
-      params.each do |key, value|
-        case value
-        when Hash
-          value = replace_param_value(value, oval, nval)
-        when Array
-          value = value.map { |o| o == oval ? nval : oval }
-        when oval
-          value = nval
-        end
-        output[key] = value
-      end
-      output
-    end
   end
 
   class ButtonField < Field #:nodoc:
@@ -210,7 +178,7 @@ module Webrat
       [".//button", ".//input[@type = 'submit']", ".//input[@type = 'button']", ".//input[@type = 'image']"]
     end
 
-    def to_param
+    def to_query_string
       return nil if @value.nil?
       super
     end
@@ -233,13 +201,13 @@ module Webrat
       ".//input[@type = 'hidden']"
     end
 
-    def to_param
+    def to_query_string
       if collection_name?
         super
       else
         checkbox_with_same_name = form.field_named(name, CheckboxField)
 
-        if checkbox_with_same_name.to_param.blank?
+        if checkbox_with_same_name.to_query_string.blank?
           super
         else
           nil
@@ -261,7 +229,7 @@ module Webrat
       ".//input[@type = 'checkbox']"
     end
 
-    def to_param
+    def to_query_string
       return nil if @value.nil?
       super
     end
@@ -306,7 +274,7 @@ module Webrat
       ".//input[@type = 'radio']"
     end
 
-    def to_param
+    def to_query_string
       return nil if @value.nil?
       super
     end
@@ -363,30 +331,32 @@ module Webrat
     attr_accessor :content_type
 
     def set(value, content_type = nil)
+      @original_value = @value
+      @content_type ||= content_type
       super(value)
-      @content_type = content_type
     end
 
-    def to_param
-      if @value.nil?
-        super
-      else
-        replace_param_value(super, @value, test_uploaded_file)
-      end
+    def digest_value
+      @value ? Digest::MD5.hexdigest(self.object_id.to_s) : ""
     end
 
-  protected
+    def to_query_string
+      @value.nil? ? set("") : set(digest_value)
+      super
+    end
 
     def test_uploaded_file
+      return "" if @original_value.blank?
+
       case Webrat.configuration.mode
       when :rails
         if content_type
-          ActionController::TestUploadedFile.new(@value, content_type)
+          ActionController::TestUploadedFile.new(@original_value, content_type)
         else
-          ActionController::TestUploadedFile.new(@value)
+          ActionController::TestUploadedFile.new(@original_value)
         end
       when :rack, :merb
-        Rack::Test::UploadedFile.new(@value, content_type)
+        Rack::Test::UploadedFile.new(@original_value, content_type)
       end
     end
 
@@ -450,25 +420,6 @@ module Webrat
       @value.delete(value)
     end
 
-    # We have to overide how the uri string is formed when dealing with multiples
-    # Where normally a select field might produce   name=value   with a multiple,
-    # we need to form something like   name[]=value1&name[]=value2
-    def to_param
-      return nil if disabled?
-
-      uri_string = @value.collect {|value| "#{name}=#{CGI.escape(value)}"}.join("&")
-      params = case Webrat.configuration.mode
-      when :rails
-        parse_rails_request_params(uri_string)
-      when :merb
-        ::Merb::Parse.query(uri_string)
-      else
-        { name => @value }
-      end
-
-      unescape_params(params)
-    end
-
   protected
 
     # Overwrite SelectField definition because we don't want to select the first option
diff --git a/lib/webrat/core/elements/form.rb b/lib/webrat/core/elements/form.rb
index 21d710b..ef627ce 100644
--- a/lib/webrat/core/elements/form.rb
+++ b/lib/webrat/core/elements/form.rb
@@ -38,15 +38,24 @@ module Webrat
       end
     end
 
+    # iterate over all form fields to build a request querystring to get params from it,
+    # for file_field we made a work around to pass a digest as value to later replace it
+    # in params hash with the real file.
     def params
-      all_params = {}
+      query_string = []
+      replaces = {}
 
       fields.each do |field|
-        next if field.to_param.nil?
-        merge(all_params, field.to_param)
+        next if field.to_query_string.nil?
+        replaces.merge!({field.digest_value => field.test_uploaded_file}) if field.is_a?(FileField)
+        query_string << field.to_query_string
       end
 
-      all_params
+      query_params = Form.query_string_to_params(query_string.join('&'))
+
+      query_params = Form.replace_params_values(query_params, replaces)
+
+      Form.unescape_params(query_params)
     end
 
     def form_method
@@ -57,47 +66,64 @@ module Webrat
       @element["action"].blank? ? @session.current_url : @element["action"]
     end
 
-    def merge(all_params, new_param)
-      new_param.each do |key, value|
-        case all_params[key]
-        when *hash_classes
-          merge_hash_values(all_params[key], value)
+    protected
+
+    def self.replace_param_value(params, oval, nval)
+      output = Hash.new
+      params.each do |key, value|
+        case value
+        when Hash
+          value = replace_param_value(value, oval, nval)
         when Array
-          all_params[key] += value
-        else
-          all_params[key] = value
+          value = value.map { |o| o == oval ? nval : o }
+        when oval
+          value = nval
         end
+        output[key] = value
+      end
+      output
+    end
+
+    def self.replace_params_values(params, values)
+      values.each do |key, value|
+        params = replace_param_value(params, key, value)
+      end
+      params
+    end
+
+    def self.unescape_params(params)
+      case params.class.name
+      when 'Hash', 'Mash'
+        params.each { |key,value| params[key] = unescape_params(value) }
+        params
+      when 'Array'
+        params.collect { |value| unescape_params(value) }
+      else
+        params.is_a?(String) ? CGI.unescapeHTML(params) : params
       end
     end
 
-    def merge_hash_values(a, b) # :nodoc:
-      a.keys.each do |k|
-        if b.has_key?(k)
-          case [a[k], b[k]].map{|value| value.class}
-          when *hash_classes.zip(hash_classes)
-            a[k] = merge_hash_values(a[k], b[k])
-            b.delete(k)
-          when [Array, Array]
-            a[k] += b[k]
-            b.delete(k)
-          end
-        end
-      end
-      a.merge!(b)
-    end
-
-    def hash_classes
-      klasses = [Hash]
-
+    def self.query_string_to_params(query_string)
       case Webrat.configuration.mode
       when :rails
-        klasses << HashWithIndifferentAccess
+        parse_rails_request_params(query_string)
       when :merb
-        klasses << Mash
+        ::Merb::Parse.query(query_string)
+      when :rack, :sinatra
+        Rack::Utils.parse_nested_query(query_string)
+      else
+        query_string.split('&').map {|query| { query.split('=').first => query.split('=').last }}
       end
-
-      klasses
     end
 
+    def self.parse_rails_request_params(query_string)
+      if defined?(ActionController::AbstractRequest)
+        ActionController::AbstractRequest.parse_query_parameters(query_string)
+      elsif defined?(ActionController::UrlEncodedPairParser)
+        ActionController::UrlEncodedPairParser.parse_query_parameters(query_string)
+      else
+        Rack::Utils.parse_nested_query(query_string)
+      end
+    end
   end
 end
diff --git a/lib/webrat/core_extensions/nil_to_param.rb b/lib/webrat/core_extensions/nil_to_query_string.rb
similarity index 65%
rename from lib/webrat/core_extensions/nil_to_param.rb
rename to lib/webrat/core_extensions/nil_to_query_string.rb
index 019290b..d609058 100644
--- a/lib/webrat/core_extensions/nil_to_param.rb
+++ b/lib/webrat/core_extensions/nil_to_query_string.rb
@@ -1,5 +1,5 @@
 class NilClass #:nodoc:
-  def to_param
+  def to_query_string
     nil
   end
 end
diff --git a/spec/private/core/field_spec.rb b/spec/private/core/field_spec.rb
index 0a7e255..a629368 100644
--- a/spec/private/core/field_spec.rb
+++ b/spec/private/core/field_spec.rb
@@ -77,7 +77,7 @@ module Webrat
 
       element    = Webrat::XML.document(html).css('input').first
       text_field = TextField.new(nil, element)
-      text_field.to_param.should == { 'email' => 'user@example.com' }
+      text_field.to_query_string.should == 'email=user@example.com'
     end
   end
 end
diff --git a/spec/private/core/form_spec.rb b/spec/private/core/form_spec.rb
new file mode 100644
index 0000000..aa28fa1
--- /dev/null
+++ b/spec/private/core/form_spec.rb
@@ -0,0 +1,51 @@
+require File.expand_path(File.dirname(__FILE__) + '/../../spec_helper')
+
+describe "Multiple nested params" do
+  it "should be corretly posted" do
+    Webrat.configuration.mode = :rails
+
+    with_html <<-HTML
+      <html>
+      <form method="post" action="/family">
+        <div class="couple">
+          <div class="parent">
+            <select name="user[family][parents][0][][gender]">
+              <option selected="selected" value="Mother">Mother</option>
+              <option value="Father">Father</option>
+            </select>
+            <input type="text" value="Alice" name="user[family][parents][0][][name]" />
+          </div>
+          <div class="parent">
+            <select name="user[family][parents][0][][gender]">
+              <option value="Mother">Mother</option>
+              <option selected="selected" value="Father">Father</option>
+            </select>
+            <input type="text" value="Michael" name="user[family][parents][0][][name]" />
+          </div>
+        </div>
+        <div class="couple">
+          <div class="parent">
+            <select name="user[family][parents][1][][gender]">
+              <option selected="selected" value="Mother">Mother</option>
+              <option value="Father">Father</option>
+            </select>
+            <input type="text" value="Jenny" name="user[family][parents][1][][name]" />
+          </div>
+        </div>
+        <input type="submit" />
+      </form>
+      </html>
+    HTML
+
+    params = { "user" => { "family" => { "parents" => {
+            "0" => [ {"name" => "Alice", "gender"=>"Mother"}, {"name" => "Michael", "gender"=>"Father"} ],
+            "1" => [ {"name" => "Jenny", "gender"=>"Mother"} ]
+          }
+        }
+      }
+    }
+
+    webrat_session.should_receive(:post).with("/family", params)
+    click_button
+  end
+end