Difficulty: Medium
Money Needed: About 200,000gp.

Another way to make large profits of money is by Coal merchanting.

First, go to Falador (a little west of Barbarian Village).+

Now, go to Falador east bank (next to Mining Guild) on an empty world such as world world 62 and buy all the coal you can for 120 - 150 gp each. Buy around 1k or more, depending on how much of a profit you want to make, then bank and note it all and transfer to world 1 (when possible).

Staying in this same bank, start selling all of your coal to people right outside the doors of the bank for 180 - 200 each! Once done, guess what? You've made yourself an easy 30-40k* profit!

*You should receive about 30-40k profit for about 1k of coal. Try buying more than 1k coal to increase your profit!