6 / 23

A soldier stands guard outside the Pemex headquarters after an explosion in Mexico City, Thursday, Jan. 31, 2013. Mexico's stated-owned oil company says an explosion at its headquarters in the capital has left several workers injured. (AP Photo/Eduardo Verdugo)

A soldier stands guard outside the Pemex headquarters after an explosion in Mexico City, Thursday, Jan. 31, 2013. Mexico's stated-owned oil company says an explosion at its headquarters in the capital has left several workers injured. (AP Photo/Eduardo Verdugo)

Mexico City oil company explosion

The Mexican government said on Feb. 4 that a gas leak caused a blast that killed at least 37 people at the offices of state oil monopoly Pemex in Mexico City, raising fresh questions about the firm's safety record.