You can trade it via most platforms that offer CFDs, just like how you trade forex. If your platform offers gold, then it probably can offer oil via MT4. In terms of volume, it is supposed to be less liquid than forex, but if you are trading fairly small contracts its easy to get filled. Just note that oil can move abuot 5-10% a day, whereas fx moves 2-3% on big days, so you can make bigger wins and bigger losses.