Theoretically the most versatile gas?

[HIGHwing]

If your implication is that the 23/20 is optimal, I'd disagree, with the 23/20 having an END of 125' vs 75' for the 18/45(O2 considered as narcotic). Why would you consider doing either without accelerated deco?

Hold on a second. I'm not saying 23/20 is the optimal gas, I'm trying to get the OP to see the difference in deco obligation in a lost gas situation. If you're mixing your own gas, you might as well optimize the O2. I picked He @ 20 because it's far closer to the OP's claimed experience level, versus some of previously quoted mixes.

It is my observation that most people don't realize the impact of a few percent of oxygen at the depth considered by the discusssion. By pushing the O2 from 18 to 23, we see a significant difference in lost gas deco. I find that interesting and it would certainly impact how I would mix the gas.

 

[boulderjohn]

Just doing some ideal quick calculations and was surprised to see that only one percentage of oxygen (18%) is neither hypoxic or toxic at any depth up to 65m.

I would not get too hung up on the hypoxia issue. I have a Shearwater Predator, and it gives me a hypoxia warning whenever my PP02 is to low. I have been doing a lot of local dives on air recently, and I am amused to get that warning as soon as I input 21% O2, while I am still on shore. That is because it adjusts for altitude. According to that standard, at my altitude, the air I breathe every day is hypoxic. I am not even really at high altitude for Colorado. When I dive in a mountain lake, the air I breathe before I get in the water is severely hypoxic. Somehow I live.

 

[ajduplessis]

I am with Kev on 20/20. It takes the edge off 60m (200ft) dives with an acceptable END 43m (140ft) that does not cost a fortune. You can stick any other gas in your mouth without ICD worries and will produce less deco than 18/45. Works for me!!