The new owner of the St. Paul Park oil refinery and SuperAmerica stores in Minnesota and Wisconsin plans an initial public stock offering.

Northern Tier Energy, based in Ridgefield, Conn., was created when two private investment firms acquired the refinery, convenience stores and a stake in an oil pipeline from Marathon Oil Corp. in December 2010.

The 14-month-old company hopes to raise $200 million in the common stock offering, part of which would be used to buy Marathon's remaining stake in a subsidiary, according to an amended regulatory filing Friday and an initial one in December.

Northern Tier operates 166 SuperAmerica convenience stores and supports 67 SuperAmerica franchises, mainly in Minnesota and Wisconsin. About 75 percent to 80 percent of the St. Paul Park refinery's output is sold through the SuperAmerica stores, the company said.

It also owns a 17 percent stake in a 300-mile pipeline that carries crude oil from a hub at Clearbrook, Minn., to the refinery. In its offering documents, the company said its business strategy relies partly on acquiring lower-priced midcontinent crude oil, which has meant higher margins for other producers.

In the nine months ending Sept. 30, Northern Tier had $3.2 billion in revenue and a net loss of $264 million, according to regulatory filings.

ACON Investments in Washington, D.C., and TPG Capital in Fort Worth, Texas, formed Northern Tier to operate the former Marathon assets. It intends to offer shares on the New York Stock Exchange under the symbol NTI.

David Shaffer • 612-673-7090