Hexagon Petroleum Refinery
Antelope Ridge, New Mexico
Spherical Oil Tanks
A couple of shots against these tanks will unmount them - unchecked, they'll roll around the arena before exploding against any vehicles they coming across. Try releasing a few of them at the same time to cause panic - as a bonus, you'll now have better access to the powerups that nestle behind them.
Each of the three drums has three powerups/crates on their roof, usually including the sought-after wrench. Getting to them is trickier - you'll need to take out the gates guarding the compound, before slowly climbing the red ramps to the top. While this is going on, enemies may try to attack - if they hit the drum it will go up, making the powerups unreachable (and taking a chunk of health off you in the process
The Refinery is made up of a series of smaller structures, many of which release powerups when destroyed - alternatively, take it out when enemies are nearby to cause additional damage.
Hidden Ramp / Secret Area
The ramp area is initially cordoned off by pipes that belch jets of flame. Simply take out the end of the pipe to cut of the fire permanently - you'll have to do this twice before reaching the foot of the ramp. Once there, you can collect several powerups and an additional one suspended in the air by Afterburning off the ramp, back into the arena.
Weapons & Powerup Spawn Points
This is a pretty small and compact level, so you can get to most powerups pretty quickly. Experts can attempt get all 9 powerups from the three drums before anyone else has the chance, but elsewhere the oil refinery, hilltops and the 'hidden' area all provide goodies.