Ttitle pretty much states it all.

I've got a craftsman 4HP 18 Gal tank compressor. The tank sits horizontally. Due to shop space issues, I'd like to prop it up vertically. Anyone see any issues with that?

What is the current and the future attitude of the pump?

It is an oil-less? I wouldn't think the tank would be the issue, but the motor and pump should probably remain upright.

It sort of looks like:
http://s7.sears.com/is/image/Sears/00916724000?layer=comp&wid=190&hei=190&fmt=jpeg&qlt=75,0&op_sharpen=0&resMode=norm&op_usm=0.5,1.0,0.0,0

It is definately oil-less.

I may actually have some instructions for it but figure while I'm trying to track those down, I'd see what the crew has to say :)

The drain cock for condensation wouldn't be at the low point any more, you'd need to relocate it or tip it horizontal each time you drain it.