The difference in actual recoil is probably none to very little (maybe a tiny bit of energy bled off but maybe not measureable. But almost every source says gas-operated guns have less FELT recoil.
From article 3:
Example: Most people feel that a gas operated semi-automatic kicks less than an O/U of equal weight using the same shell. Yet the formula has them both producing the same amount of free recoil, so how can this be? Simple.
The gas gun delivers exactly the same amount of recoil, but it does it over a much longer period of time due to the mechanism involved. The O/U gives you a punch (all the recoil at once), while the gas gun gives you a push (same recoil but delivered over more time).
Not a direct comparison to recoil operated, but says gas operated reduces recoil.
From Number 4:
With magnum loads, excess gas is vented out the lateral vents in the piston, substantially reducing felt recoil over inertia- or recoil-operated systems.
Direct as you can get statement.
From Article 5:
For comparison purposes, I shot a Super Black Eagle and a Super Black Eagle II side-by-side. The difference in felt recoil and recovery time with the Mark II was phenomenal, proving that you don’t need a gas system to tame recoil.
Why would you need a gas system to reduce recoil if a gas system didn’t reduce recoil?
A couple more, this one from http://www.sportingclays.net/forums/thread.cfm?threadid=779&messages=21
The Beretta 390, 391, Benelli, and the Browning are fantastic top of the line semi autos, you can’t go wrong with any of them. The CD is a cheap semi auto that is not even comparable to the above. Whoever said that “the 390 wasn’t so good” is spewing garbage and has no credibility. The gas operated gun(Beretta, Browning Gold) will have less recoil, and the recoil operated gun (Benelli, Browning A5) will be easier to keep clean. I don’t know if you can say which one is better, it’s more a matter of personal preference.
And a few in this post:
http://www.shotgunworld.com/bbs/viewtopic.php?t=659
Actually, I thought it was just a well known and accepted fact that gas guns shoot softer than recoil autos or pumps, I am surprised to even hear anyone disagree. You have any data or opinion other than yours to back up your argument? I see you have personal opinion that the SBE has very little recoil. Let me guess, do you have a Benelli SBE? I have a Benelli inertia operated gun, I think it is a great gun and would easily buy another. Does that mean it can’t have any negatives?