Top television networks have teamed up to create a technology standard that they say will make it easier for them to sell targeted advertisements, the latest collaborative effort from a historically competitive industry.

Called Project OAR, an acronym for “Open Addressable Ready,” this consortium will work to create and implement watermark technology designed to help TV programmers send targeted ads to people with smart TV sets.

For example, one household might see an ad for a Ford Motor Co. truck, while a neighbor watching the same show at the same time might see an ad for a Ford sports car. The group expects to finish work on the watermark technology by next year.

Today, a TV network typically relies on a cable or satellite TV operator to send different ads to households. The watermark would make it easier for the networks to control a greater part of that process, at least for households with internet-enabled TV sets.

It is one of many steps that could give the TV networks’ vision of countering digital ad giants like Facebook Inc. and Alphabet Inc.’s Google a chance to reach fruition.

Programmers in the consortium are Walt Disney Co.’s Disney Media Networks, Comcast Corp.’s NBCUniversal Media LLC, CBS Corp. , Discovery Inc., AMC Networks Inc., Hearst Television Inc. and AT&T Inc.’s Turner. AT&T ad group Xandr and Comcast’s FreeWheel have also joined.

Inscape, a data company owned by TV manufacturer Vizio Inc., will develop the watermark standard with input from consortium members, the group said. Vizio will equip its TVs to read the watermark; the group will ask other TV makers to do the same.

TV networks now are working together to try to compete with online ad providers and appeal to marketers struggling to reach their increasingly elusive consumers.

In recent years, they’ve made strides in helping advertisers select shows that are more likely to reach specific audiences—soda drinkers or people in the market for a minivan, for example—rather than merely selling by traditional demographics such as age and gender.

OpenAP LLC, another effort from a separate consortium of media companies, has created a standardized system that enables advertisers use the same data sets to inform their media plans across networks. NCC Media, an organization backed by cable giants like Cox Communications Inc., Charter Communications Inc. and Comcast, also is working on capabilities to use data in advanced TV ad buying.

Some media companies, including AT&T and AMC Networks, also have announced plans to create more targeted TV ad opportunities for marketers.

Write to Alexandra Bruell at alexandra.bruell@wsj.com