MEXICO CITY - Increasingly sophisticated thieves stole about 20,000 barrels per day of oil products from Mexico's state-owned oil company in the first four months of 2011, thefts worth about $250 million, the company's director said Thursday.

Juan Jose Suarez Coppel, the head of the Petroleos Mexicanos oil company, says that was more than thieves stole in all of 2010. The company is better known as Pemex.

Suarez Coppel said the stolen fuel was the equivalent of 100 tanker trucks per day.

"Fuel theft has increased in the last few years," said Energy Secretary Jose Antonio Meade. "The gangs that participate in these crimes are increasingly sophisticated, better organized and many times they have carried out these thefts using the latest technology."

Mexican officials say drug cartels have been involved in the thefts, often by tapping into state-owned pipelines. The thieves will sometimes inject water into pipelines to cover up the drop in pressure caused by thefts or drill a second tap near the first to continue siphoning off oil if the first is detected.

Drilling into pipelines is dangerous because of the high pressure and combustibility of the fuel; while illegal pipeline taps have caused explosions, fires and spills in the past, authorities still find hundreds of successful taps each year.

Suarez Coppel said 556 illegal taps had been detected so far in 2011, compared to 710 in all of 2010.

Officials have said in the past that drug cartels have been implicated in some of the thefts, especially in northern Mexico. Suarez Coppel said the largest number of thefts - about 150 - occurred in Sinaloa state, considered the cradle of Mexican drug trafficking. He said the cartels may sell the fuel or even use it for their own vehicles.

About 390 of the taps involved refined fuel pipelines, while about 135 were at ducts carrying crude. Because there is little market in Mexico for unrefined oil products stolen from some pipelines, the thieves often sell the oil products to US refineries.

Pemex filed lawsuits in May against nine US companies for alleged involvement in buying or processing Mexican oil products.

But thieves have also sold unrefined fuels to bulk users like brick kilns and factories, so authorities have proposed new laws that would stiffen penalties for the possession, sale or use of stolen oil products.

The changes being discussed in congress would also allow organized crimes charges to be brought in fuel-theft cases, and allow charges to be brought against Pemex employees or subcontractors who give information to thieves.

In the past, investigators have said workers may have told thieves when pressure in pipelines would drop for maintenance or other reasons, allowing them a window of opportunity to drill into ducts more easily.

Pemex officials did not answer questions about whether that lost production has been recovered.