I have never seen gas used for rat control and have not personally used gas for any pest control. I have corresponded with researchers that have done studies on gas vs bait for gopher control. The general consensus was that use of gases and gas bombs are less effective and more dangerous than baits. Many gases and gas bombs were tested. Of the gas products tested, methyl bromide, chloropicrin, and a nitrocellu-lose film bomb gave the highest percentages of kills. About half the gophers succumbed to gas and gas bombs. Baits were found to be more cost effective than poisons. Compared to poison baits, the cost of poison gases is excessive, even more so when labor and equipment costs are added. Cost of materials was almost negligible in bait poisoning. Success in poisoning with baits was believed to be attributed to high acceptance of baits by gophers who seem to be readily attracted. Gophers were easily lured by any poisoned bait. I expect more studies have been conducted which would yield more information. I am just guessing but would expect similar results in gas vs baits in rat control. Additionally baits for rats can be placed in bait stations. Of course there are inherent dangers of using poison baits. I have used snap trap box sets and poison bait stations around quail raising facilities with good results. Rat control is perpetual.