Single-engine aircraft aren't killing people offshore, anywhere. According to the International Association of Oil & Gas Producers, for the period from 1994-1998, the number of fatalities worldwide due to engine failure in helicopters was exactly zero. For airplanes, the number is much higher, & engine failure is the biggest cause of fatalities. For helicopters, it's FITWO (Flight into Terrain, Water, or Obstacles, what the US calls CFIT), midair collisions, & other mechanical failures. I don't recall a single fatality in the Gulf of Mexico in the last 20 years due to engine failure, & there are far more single-engine aircraft flying than twins. Fatalities yes, but not from engine failure.
See for yourself:
Safety performance of helicopter operations in the oil & gas industry
I like twins, but the economics don't show the necessity, & don't kid yourself, it's always economics. The only bearing safety has for corporations is economic - if they make more money (or lose less) by being safe, they will, but it's purely economic. Money talks, & everything else walks. It's wrong, but that's the way it is.