With the new oil rig explosion in the gulf it seemed like a good time to try and get a handle on just how frequent these types of problems were.
An Study based on MMS data covering 1992 to 2006 found the absence of fatalities encouraging. The study covered drilling on the outer continental shelf. It found that in the current study period had a blow out rate of 1/387 versus 1/246 in the earlier 1971-1991 period.
It noted that shallow gas influx were a continued hazard, and that there was an increase in cementing problems. Of the 15,077 possibles, there were only37 blow outs. This puts the catastrophic blowout percentage somewhere around the .0006% mark. The problem with these small numbers is that people can go for very long periods (whole careers) with no negative incidents. So there is always the incentive to cheat.
You see this frequently in OSHA compliance in construction sites. Safety compliance is usually strictest with large corporations who know that the laws of many small numbers will catch up to them if they operate in an unsafe manner. They can either be the contractor themselves, or it can be the client. There are also areas where the regulating authority is strict in its enforcement.
This increases the number of "negative incidents" to the operator for operating unsafely beyond the fraction of a percentage point, and thus makes it worth their effort to avoid negative consequences.