"The order to begin a national campaign of punishing the interests of the oligarchy and this illegitimate government has been put in play.." EPR Web site message after the attacks.
Mexico's Popular Revolutionary Army (EPR), a splinter of the original group formed in 96 (in south-west Mexico), blew up a PEMEX 36-inch natural gas pipeline that shut down two auto assembly plants (Nissan/Honda) in Guadalajara. Two other pipelines were shut down (gas and crude oil) affecting the Salamanca oil refinery (domestic production).
The operation was small, and according to the group required eight charges set by small teams in three locations. The charges were set with a time delay (to detonate on the 5th and the 10th in the early morning). Nobody was caught and there were zero casualties. I suspect the returns on investment for the attacks, particularly given their ability to impact just-in-time production facilities, were amazing.
Update:Update 2: Nissan's Aguascalientes factory produces 1,300 vehicles daily. Honda produces 120 Accord sedans daily. Further, the attack on the natural gas pipeline was on a valve complex (a particularly good systempunkt).