Ideally, olive oil is used to fuel the flames, and a beeswax candle for the Shamash. [If these are not available, one should use a type of oil or wax candle that burns a clear flame. If this is not possible, any type of oil or wax candle may be used.]
The Menorah may be prepared with oil remaining from the previous night.
Before kindling, one ensures that the Menorah has sufficient fuel to last the required duration – at least 50 minutes in total, and at least 30 minutes after Tzeit Hakochavim (whichever is longer).
Some candles manufactured for Chanukah typically burn for only half-hour. If these are lit before Tzeit Hakochavim, one would not be able to recite the Brachot. Furthermore, even if lighting after Tzeit Hakochavim, such candles tend to burn for less than half-hour in a warm environment. Therefore, longer lasting candles should be used. [When necessary, there is room to be lenient for a child under Bar Mitzvah who is unaware that the candles are burning less than they should.]
If one realized after lighting that there is insufficient oil, he should not merely add more oil. Instead, he must extinguish the flames, add more oil, and then relight the flames without the Brachot.
