As vhfg says, bit of a depends question, but on the whole correct. For example, the High Tension leads on a car engine (which work the spark plugs) run at about 12,000 Volts (can't remember the amperage). You can get an uncomfortable belt off them, but it won't kill you, whereas a domestic cooker runs at 240Volts , but around 30 amps and that could conceivably kill you.
If you imagine a hose pipe then the volts are the pressure and the amps are the amount of water Ie the thickness of the pipe. So it's a combination of the 2, ie you need enough pressure but you also need enough water.
Only a tiny current to kill you through 'ventricular fibrillation'. Here, heart muscles are affected by the current and move independently of each other. This means the heart no longer acts as a pump. A tenth of an amp (100 mA) can do this. Under certain conditions, and according to the sensitivity of the victim, it could be as low as Priceyclause's 30 mA.