Pemex filed the new complaint in a court in the Southern District of Texas on April 10, after a judge ruled Mexico's oil monopoly could not add the Shell subsidiaries and other companies, including ConocoPhillips (>> ConocoPhillips), to an original claim filed in 2010.

Pemex's exploration and production arm (PEP) claims the companies traded or transported upwards of $300 million of natural gas condensates, which can be refined into high-value oil products, that it says were hijacked by criminal gangs linked to violent Mexican drug cartels and smuggled across the U.S.-Mexico border.

"Some of the defendants knew, or at least should have known, they were trading in or transporting, stolen condensate," the court papers said. "Others were ignorant that they were purchasing stolen goods. In either case, however, the defendants took possession of Mexico's sovereign property."

Mexico's oil resources are nationalized and Pemex is controlled by the government.

The new case, which is almost identical to the original 2010 filing, alleges the U.S. trading arm of Shell, STUSCO, was the largest marketer of the condensate, trading at least $150 million of the fuel but without knowing it was stolen.

It says ConocoPhillips bought at least $35 million in stolen fuel from third parties, also with no knowledge of the condensate's illicit origin. Shell officials were not immediately available for comment. ConocoPhillips officials said it would not comment on ongoing legal matters.

A judge overseeing the 2010 case ruled earlier on April 10 that both companies, along with FR Midstream Transport, Marathon Petroleum Company and Sunoco, could not be added to the suit because it would result in excessive delays to the case.

Lawyers for PEP and Pemex representatives in Mexico City did not respond to requests for comments.

PEP claims that at times the thefts reached up to 40 percent of condensate produced at the Burgos field, which spans the Mexican states of Tamaulipas, Nuevo Leon and Coahuila.

The gas field has been menaced by powerful drug gangs branching out into new illegal rackets in search of more revenues. Drug violence in Mexico has killed more than 50,000 people in the past five years and Pemex workers have been kidnapped and intimidated by the gangs.

(Reporting by Mica Rosenberg; Editing by Simon Gardner and Matt Driskill)

By Mica Rosenberg

Stocks treated in this article : BASF SE, ConocoPhillips