At my favorite dive shop they are always asking divers if they want to do an introductory Nitrox dive. The deepest that they go is on a couple wrecks which are a maximum 125 feet to the sand and the dives usually lasts for 45 minutes to an hour with about 30 minutes bottom time. The deepest reef dive is about 95 feet up to 25 feet. With an AL80 I'll usually have at least 1000psi left over on the wreck dives and upwards of 1000-1400 on the shallower reef dives depending on how deep it is. Several times we have double-dipped a wreck with an hour SI, same results. Now I understand that there is a profit motive for the shop if they can sell a customer on a Nitrox card, which is OK. My point is that I usually dive with a group of six or less with a DM and either we'll come up or buzz around close to the boat when the worst airhog is low on air or our time is up. I do only two dives in the morning trip as it's too tiring for me at my age, 70, to go out twice in the same day though I have gone out with them on night dives and then did the afternoon dives the next day. So the question is how would using a gas mixture benefit me? If I used Nitrox on the morning dives do you think it would help me with my energy level for the afternoon dives?