Am a commercial Diver in Canada fishing Swimming Scallops using divers in depths of 70 to 90 ft ...I've done this since 1982... all on Air about 15000 dives in that time... last year I decided to buy a Nitrox system ..I live in an Isolated area in BC so buying Nitrox fills was not an Option ....I took a Nitrox course as did the two divers who work for me and after much research bought a membrane system ...when the Nitrox system arrived I started off using 34% soon 36% and now 38% when I felt comfortable using Nitrox ... this works great but wouldn't go beyond 38% with the depths I dive ...with Hundreds of dives on Nitrox ...(we use two tanks a day ) we all certainly feel much less fatigued than using Air and Generally all around better! ...you don't get out of breath when the tide starts running and your working harder either...I'm sold on Nitrox and will never dive air again ...it really does make a big difference in how one feels after diving