The next chapter in the four-part campaign, dubbed "Bringing Down TransCanada's House of Cards: The Keystone Chronicles," shows the Democratic mega-donor in Mayflower, Ark., where an underground ExxonMobil oil pipeline burst in March.
In the ad set to air during this weekend's U.S. Sunday morning political talk shows, Steyer makes the case that pipelines pose a real and present danger to anyone living near them.
Residents of the lakeside Arkansas community say they're still suffering health effects after an estimated 5,000 barrels of oilsands crude seeped from the pipeline and through a residential neighbourhood. One of the Mayflower home-owners who lives down-wind from the spill appears in the commercial.
"He was quite moved by what happened to these people," Mike Casey, spokesman for Steyer's NextGen Climate Action, said in an interview Thursday. "The people who got it the worst in Mayflower weren't the ones whose basements were flooded; they were they people who lived down-wind and were exposed to air-borne toxins."
State and federal officials have filed a lawsuit against ExxonMobil seeking penalties under the Clean Water Act. In response, ExxonMobil has said Arkansas hasn't proven that waste from the spill and cleanup is hazardous.
"We know from Mayflower that these pipelines burst at the worst times in the least-prepared places, rural communities with little to no spill management infrastructure," Casey said.
"If the oil industry is so certain that it's not going to create more Mayflowers, why don't they sign a legally binding document that exposes them to criminal liability, or forces them to cover cleanup costs, when their pipelines rupture?"
Steyer, a former hedge fund manager who quit his life's work to become a climate activist, is an emerging nemesis to Calgary-based TransCanada and the oil industry as the U.S. State Department continues to assess Keystone XL's merits.
U.S. President Barack Obama's ultimate decision on the pipeline isn't expected until early 2014. At a Democratic fundraising dinner at his home in San Francisco in April, Steyer pressed Obama to reject Keystone XL.
The slick inaugural ad of Steyer's ad campaign raised the ire of the oil industry due to his insistence, as he stood at a Texan refinery, that the Alberta oilsands bitumen to be transported by the pipeline is destined for foreign markets. Foreign oil companies, he alleged in the commercial, will make almost $4 billion thanks to Keystone XL, including Chinese firms.
"Foreign countries will get more access to more oil to make more products to sell back to us, undercutting our economy," he says in the ad. "Here's the truth: Keystone oil will travel through America, not to America."
Not so, says a pro-pipeline group.
"Perhaps what makes Steyer’s claims so outlandish is that they completely ignore what's happening today when it comes to exports," the Oil Sands Fact Check organization said in a detailed statement aimed at debunking Steyer's claims in the ad.
"Separate and apart from Keystone XL, thanks to our recent oil and gas boom, the United States has been exporting refined petroleum products, like diesel, that don't have a strong market in the United States — and this has preserved jobs and strengthened the economy."
TransCanada also responded in point-by-point detail to the ad — making note of the billionaire's past investments in the oil industry.
"As a businessman, Mr. Steyer would have relied on the facts before making investment decisions — whether it was in a distressed company, an international energy firm (like BP) or an energy transportation company involved in the oil sands (as his previous firm invested heavily in and he has profited from)," the company's Shawn Howard said in a statement.
"But when it comes to Keystone XL, Mr. Steyer and his advisers have chosen to ignore the facts."
Many of his arguments make little sense, Howard added.
"What does make sense is to use the Canadian and American oil that Keystone XL will transport to serve domestic markets first, decrease transportation and energy costs while reducing dependence on more expensive and potentially unreliable imports," he said, adding that China "has not received a single drop" of oil from the U.S. in at least eight years.
Steyer’s commercials begin airing two months after the pro-pipeline American Petroleum Institute launched its own TV and online advertising campaign heralding Keystone XL as a major job creator in the U.S.
Casey mocked those job creation claims, calling it the "big lie" told by pipeline proponents.
The Keystone pipeline would carry almost a million barrels a day of Alberta oilsands bitumen, as well as shale from the American MidWest, through six U.S. states to Gulf Coast refineries.
Obama says he won't greenlight the project if it's found to exacerbate global greenhouse gas emissions, and mocked suggestions by Keystone XL proponents that it will create tens of thousands of jobs in an interview with the New York Times over the summer.