Unified marketplace for advertisements and content in an online system

A system comprising:

• a processor and a memory;
• an advertisement storage device configured to store data defining a plurality of advertisement items originating with advertisers;
• a content storage device configured to store a plurality of content items originating with sources other than advertisers;
• and
• a server system in data communication with the ad storage device and the content storage device and configured to display advertisement items retrieved from the ad storage device and content items retrieved from the content storage device as a stream of graphical or textual items arranged in a sequence on a web page and viewable by a user on a user device, the server system further configured to determine respective bid amounts for respective advertisements items and to determine a respective content bid amount for respective content items that allows ranking together the respective advertisement items and the respective content items, the server system further configured to compute respective ranking scores for the respective advertisement items using the determined respective bid amounts and to compute respective ranking scores for the respective content items using the determined respective content bid amounts, the server system further configured to order the ranked advertisement items and the ranked content items together in the stream using the respective ranking scores computed for each respective advertisement item of the plurality of advertisement items and each respective content item of the plurality of content items, the server system further configured to transmit a web page including the stream to a user device over a network.