Many restaurants filter and reuse deep fryer oil so why not at home? After its first use strain through a muslin, coffee filter or cheesecloth to remove all the crumbs and left-over material and then store in the freezer.
Do not reuse cooking oil if rancid, smells or produces smoke. Apart from the odours and odd flavours it may produce carcinogenic free radicals (see antioxidants). Careful straining and preparation and allowing to cool before placing in the fridge or freezer should allow one safe reuse and cut your costs in half!
Or use it to power your car and cut your fuel bills
If you use vegetable oil and have access to worthwhile amounts you could be using it to power your car or other diesel automotive engine. The process is straight-forward although you should check with the engine manufacturer if your particular engine can run on bio-diesel first.
Bio-diesel is less expensive, renewable clean-burning fuel. Creating it from used cooking oil requires rudimentary processing and the ability to measure and mix several liquids. For further information search How to make bio diesel, there are many detailed instructions including videos on YouTube.