Sunday morning quarterbacking...

The theft is both a symbolic and financial blow to the Mexican government. Taxes paid by Pemex account for 40 percent of the federal budget.
Mexico's oil industry is already in the hurt locker due to their fields becoming less and less productive, so any additional dents in this business which accounts for 40% of their federal budget is a significant risk to Mexico's National Security.

Mexico has launched an all-out campaign to defend the pipelines, drawing in the army, the attorney general's office, the Interior Ministry and the customs service. During the past two years, the government has conducted helicopter overflights, installed electronic detection devices inside the pipelines and beefed up Pemex's private security force.
Security forces guarding pipelines are not chasing drug cartels, so this is a double win for the cartels (oil profits and diverting security forces)

Suárez estimates that Pemex will spend hundreds of millions of dollars over the next three years defending its pipelines. With the company's maintenance staff overwhelmed, Pemex assembled 20-man teams this year to repair breaches caused by theft.
Who pays for this in the long run? Oil prices will have to go up, so the Cartels will even make more money.

Pemex sent out a call for help to the federal government in 2007. In June that year, Mexican customs officials informed U.S. Immigration and Customs Enforcement (ICE) that they had discovered dozens of Mexican companies that appeared to be conspiring with U.S. firms to export stolen petroleum products across the border.

Working closely with the Mexican customs service, ICE investigators said, they soon uncovered a network of Mexican and American companies that shipped stolen oil to the United States in tankers, stored it in aboveground containers in Texas and then shipped it in barges to end users in the United States.

With oil prices then at record highs, the scheme allowed U.S. companies to buy petroleum products at below-market value.
Of course oil prices are not currently at record highs, and they have been falling (although that is forecasted to stop soon), so I wonder if oil prices decrease enough if it will make illegal sells unprofitable, or not worth the risk? However, decreased oil prices would probably hurt the government of Mexico even more.

U.S. companies in bed with organized crime? Who is really surprised?