After 4 vo2 max tests I got my own watts to oxygen consumption equation that predicts my oxygen usage within 1% percent accuracy. Works all the way from 100 watts to vo2 max (~400 watts for me).
Watts = ( Absolute Vo2 (L/min) - .9579) / .0095
Absolute Vo2 (L/min) = .0095*Watts + 0.9579
My best 30' power record this past Spring was 340 watts. That puts me at 4.19 L/min, or around 89% of my vo2 max, 4.7L/min.
Lance's 30 minute, 495 watt record breaking effort up the Galibier in 2003, according to my equation, would have taken 5.66 L/min. That's 90% of his vo2 max, 6.3L/min. His relative vo2 max is 84 L/kg-min. That seems about right according to the net.
Anyone with numbers care to see how close it works for you?