Quicksilver is correct however it depends which name you register as different countires are responsible for allocating names etc. So if you register a co.uk it's done for 2 years not one.
You can of course pay in advance and secure it on a long term basis which generally gives a good discount.
Hi i would like to share my experience with you .I have purchased one domain from the site http://www.9cubehosting.com/ .Here i am paying fee yearly once and i am doing renew my domain yearly once .If i paid for one year means it will guaranteed me to be mine for that one year .