Throughout 2018, prominent tech companies that double as lucrative advertising networks started making political ad buyer data available to the public. That meant anyone could see who, exactly, paid for any campaign ads on Facebook, Twitter or Google.

New data published by New York University researchers found that left and right-leaning groups are buying ads in different places.

The study, published by NYU’s Tandon School of Engineering, examined how much different political groups are spending on Facebook, Twitter and Google ads. Based on analysis of nearly 900,000 ads, it seems the left prefers Facebook and Twitter, while the right prefers Google for ad spending.

Rep. Beto O’Rourke, a Texas Democrat who will try to dethrone Sen. Ted Cruz in the upcoming midterm elections, was the top campaign spender on both Facebook and Twitter. That election is one of the most high-profile of the upcoming midterms. As such, O’Rourke was the biggest ad buyer across the three sites that NYU could find. The Democratic candidate spent $683,000 on ads, according to the study.

The top spenders on Google were on the opposite side of the political spectrum. Four of the five biggest Google ad buyers were right-of-center, including the right-wing Senate Leadership Fund and the Koch Brothers-backed Americans For Prosperity. However, O’Rourke still spent $214,000 advertising on Google.

The study was an expanded version of similar data published by NYU Tandon earlier this year. That earlier study examined the top ad buyers on Facebook, finding that President Trump was the most prolific political advertiser on the site. The new data suggested Trump still has the highest total number of ads, with a large majority of them being targeted at small groups of people.

However, Trump’s digital ad effort was mostly relegated to Facebook. The president only had 27 ads on Google and none on Twitter.

Facebook in May became the first of the three studied platforms to reveal who bought political ads, while Twitter and Google would later follow suit. Facebook was, by far, the most popular of the three in terms of total ads, ad spending and impressions. The social network giant accounts for a quarter of digital advertising revenue in the U.S.