typically 5 wt, you can experiment with other weights, I used a redline "like water" oil in a 125 shock and have used 7.5 in hillclimb bikes. there is no specified volume, you will make a mess and you want to make sure there is no air in the oil cavity. these do not use a piston like a Sachs or some Ohlins, they have a bladder, If you are unsure you may want to get a manual or take it to someone that knows what they are doing, these are not like forks and done wrong can make your bike suspension perform poorly. you will also need a nitrogen bottle, gauges and hardware to get the pressure up to approx 165 psi, do NOT use air