You can easily get whatever you want at Gatwick though that is outside the coverage of the Oyster Card, which kicks in around East Croydon - buy a train ticket to East Croydon and use the Oyster Card from there but you would have to get off the train there to wand your Oyster Card and get back on I think.

I have never done the above but heard from others who say it is possible. Easiest just to buy a regular train ticket and buy your Oyster Card at the first tube station in London when you want to ride.

benefit of gatwick and having to purchase a train ticket is you can then take advantage of the 2for1 deals - another major confusing topic.

I am going in March and our plan is to buy our round trip train ticket and a 7 day travel card - for travel in London....

Buy your return (round trip) GHatwwick ticvket upon arrival and you're covered for the infamous 2 4 1's.

For 4 days, I'd get at the Victoria tube stop the PAYG oyster card....put say 25 quid on it (there will also be a 5 quid deposit) for each of you and you're covered. You can monitor usage easily enough each time you ride the tube and if you start running low, top it up. Whatever you have left over when leaving can be refunded at Victoria before boarding the Gatwick Express back to Gatwick.

Simple indeed in this case.

The Visitor Oyster Card's activation fee is non-refundable, so the regular Oyster you buy in London makes more sense.
Also, I believe you cannot load a 7-day travelcard onto the Visitor Oyster.

For 4 days you dont need a 7 day travelcard.

Agreed - get return train tickets from Gatwick so that you can use them for the 2for1 deals and then buy a regular Oyster card at any underground (tube) station you arrive at once you get to London proper and add on some cash like someone suggested above. Before heading back to the airport return your oyster to get a refund on the card deposit and I believe any remaining balance.

www.daysoutguide.co.uk will explain the 2for1 deals. Be sure you dont put your paper ticket from Gatwick into the barrier when you leave or it might be 'eaten'. Ask the guard (they are at all stations where the gates are closed) to let you through as you want to keep your ticket.

Very helpful - thank you everyone!

And you can take the Southern line trains from Gatwick to Victoria or London Bridge instead of the Gatwick Express - you'll save a ton of money and the time difference is about 2-3 minutes, maximum.

Although the G'Ex is on a "faster" train with no stops, it travels through the most heavily trafficked rail areas of the UK (Clapham Junction and East Croydon are the two busiest stations in the UK that are not in London) so the ride to Victoria is not much quicker (29-31 minutes v. 33). If you're temporary residence is closer to London Bridge station, definitely take the Southern line train there (30 minutes).

Check out my post about 2-for-1 cards. Although it is over a year old, the basics probably are pretty much the same...though I welcome corrections/updates.

http://www.fodors.com/community/europe/special-2-for-1-days-out-coupon-thread.cfm

...and I, too, recommend Southern Railway to Victoria (if that is where you are headed)instead of the Gatwick Express. Plus, there is a TFL office in Victoria station where you can buy your Oyster card.

SS