So far, President Obama is far outpacing former Massachusetts governor Mitt Romney in the online ad wars.

President Obama speaks at an election campaign event in Baltimore on June 12, 2012. (Jewel Samad/AFP/Getty Images)

Obama’s reelection campaign has consistently bought more search terms than Romney’s campaign, according to ComScore. In April, Obama spent three times as much on search.

Paid search ads are what appear on the top of a search engine , such as Google or Bing, when you search for a term. For example, if you search “Barack Obama,” you are likely to see an ad for the president’s campaign on the top.

That doesn’t mean Obama is spending three times as much on search ads as his rival. Ad costs vary depending on the popularity of the term — for example, a term like “student loans” will be more expensive than “Obama student loan policy.” Campaigns (and other advertisers) bid on terms, offering what they think they need to in order to get top billing. They are then charged by the number of clicks they get from the term.

Both candidates invested most of their money in terms related to their own names. But during the Republican primary, Romney was bidding on Rick Perry and Rick Santorum, says ComScore’s Eli Goodman. And Obama has bid on the DREAM Act, Obamacare and Solyndra. Both candidates have bid on terms related to health care.

ComScore also looked at online display ads — the ones that appear on Facebook and other Web pages. ComScore found that in April, Obama’s campaign delivered 865 million ad impressions online — while Romney’s delivered only 26 million.

ComScore makes projections based on people who allow the company to track their online behavior — a million in the United States — along with data from Web sites that display ads.

A recent CNN analysis found that Obama is spending twice as much as Romney on online advertising. Zac Moffat, Romney’s digital director, told the network that spending would ramp up as they got closer to the general election.