TransCanada, the company seeking to build the project, has spent more than $100,000 advertising its message to South Dakotans in recent months.
The company paid to air more than 800 television and radio spots over the last three months, according to an Argus Leader survey of political advertising disclosure forms filed with the Federal Communications Commission or included in public inspection files.
The company also bought ads in newspapers, including the Argus Leader, through the South Dakota Newspaper Association. David Bordewyk, the association's general manager, said details of the developer's advertising purchases were proprietary and would not be shared.
TV and radio broadcasters who use public airwaves are legally required to disclose information related to advertising for any political issues or candidates.
Most of the advertising aired in the Rapid City market, which is closer to the proposed pipeline route than Sioux Falls, where some ads also ran.
TransCanada spokesman Mark Cooper said the campaign is a way to dispel myths about the pipeline and provide more information about the project to South Dakotans. He confirmed the company has spent between $100,000 and $200,000 on advertising in South Dakota.
"The bottom goal is that there are various modes of communication (so) that people can better understand the project," Cooper said.
Opponents of the pipeline project have relied on a more grassroots approach to getting their message out, largely through events and social media.
John Harter, a rancher and a member of Dakota Rural Action, which opposes Keystone XL, said the group discussed running ads but nothing came of it.
As for the TransCanada advertisements, Harter said they're meant to fool the public into thinking the pipeline is both safe and needed.
The state's Public Utilities Commission will hear from the public and from all sides of the debate this month in a series of hearings.
The first will take place at 5:30 p.m. Monday in Room 414 of the Capital Building in Pierre.