We've had three separate chevy express cng vans experience significant releases of compressed natural gas on eight separate occasions over the past three years. the releases occur while fueling the vehicles in very cold weather. gm has replaced some of the cng tanks, but the releases continue to occur. gm believes the releases are related to cng tank valve o-ring failures, but they have made no formal response at this point. two of our vans have been idle for weeks as a result of the leaking tanks. *tr