By Christian Berthelsen 

A U.S. regulatory judge ruled that BP PLC manipulated the Texas natural gas market in 2008 and then conducted an inadequate internal investigation, and said fines against the British energy company could increase because the scheme took place after earlier market manipulation.

BP was accused of flooding a delivery point for natural gas in the Houston Ship Channel, sustaining losses and pushing down prices to benefit a related trading position in financial derivative markets. Enforcement lawyers from the U.S. Federal Energy Regulatory Commission sought fines of nearly $50 million for the activity, even though the government's own evidence showed the company made less than $250,000 in profits.

BP didn't immediately respond to a request for comment Thursday.

The amount of the fine being imposed on BP wasn't decided by Administrative Law Judge Carmen A. Cintron, according to the ruling released Thursday. The full FERC commission will decide on a penalty amount after reviewing the judge's conclusions.

The judge noted in her ruling that BP could face increased penalties because the conduct occurred less than five years after the company settled charges by the U.S. Justice Department and the U.S. Commodity Futures Trading Commission related to manipulation of the propane market, and violated the terms of a CFTC injunction barring it from further market manipulation.

The case was kicked off after one BP trader called another on a recorded line and asked how to describe their market strategy in a way that didn't "make it sound like we're manipulating" the gas market. The judge called the market strategy a "classic case of physical for financial benefits," and called BP's internal investigation of the matter "ineffective and biased."

Write to Christian Berthelsen at christian.berthelsen@wsj.com

Access Investor Kit for "BP plc"

Visit http://www.companyspotlight.com/partner?cp_code=P479&isin=GB0007980591

Access Investor Kit for "BP plc"

Visit http://www.companyspotlight.com/partner?cp_code=P479&isin=US0556221044

Subscribe to WSJ: http://online.wsj.com?mod=djnwires