Amazon is considering adverts for its Kindle ebook reader, patents have revealed.

The online retailer has filed patent applications "On-Demand Generating E-Book Content with Advertising" and "Incorporating Advertising in On-Demand Generated Content" that would deliver contextual ads to readers as they perused the electronic content.

An example given is that restaurant adverts could be shown when a character in a novel is dining out or that tourist boards could advertise when relevant locations get a mention.

Amazon is looking at placing ads in a variety of content, including out-of-print material, where the books "typically do not include advertisements and, if they do, the advertisements are out of date and inapplicable".

The patent describes the ad system as opt-in with the possibility of cheaper content for those that accept the ads. From one patent:

"Including advertising and/or related content with on-demand printed content may prove advantageous to a consumer. For example, a lower price may be offered to a consumer regarding a request for on-demand printed content if the consumer is willing to accept advertising in the printed content".