Used to be, if you wanted to save money on your summer vacation, you gave up the convenience of flying and drove to your destination. A couple tanks of gas cost less than airfare in those days.

Now, with gas approaching $4 a gallon in many areas of the country, and some experts predicting it will reach $5 a gallon by the end of the year, finding cheap flights online could be a lot more cost effective than ever before. And when you consider the speed and relative convenience of flying, taking to the air – rather than driving – may make more sense for your summer vacation.

Still not sure? Check out an online fuel cost calculator to see just how much that road trip will cost, versus flying.

When it’s time to find cheap flights, there’s no faster, easier and more cost-effective way than going online. Websites like Expedia.com offer instant access to low-priced fares for domestic and international travel.

You can also ensure you snag the cheapest airfare available by following a few simple booking rules:

* Time your purchase – If your vacation dates are set in stone, book your flight as early as possible, especially during peak travel times. Usually, as a travel date approaches, airfares rise in price. Wait too long and you could find yourself paying through the nose or unable to obtain tickets for the travel days you need. If, however, your vacation dates are flexible and you can be ready to fly on a moment’s notice, it’s sometimes possible to score deep discounts at the last minute. Be forewarned, however, this is a risky game – one you might not want to play if you’re traveling with kids who will be disappointed if you have to cancel.

* Shop around, but sensibly – You can find plenty of websites that claim to sell cheap flights, so it makes sense to comparison shop – within reason. If a deal seems too good to be true, or you’ve never heard of the seller website before, or you can’t find a phone number to call or some way to connect with an actual human being when you have a problem – you may find out the deal is not so great after all.

* Flexibility pays off – Fares vary based on departure and destination airports. If you’re able to drive a short distance to or from a different airport, you might find a cheaper fare. Also, when you travel makes a difference. Certain times of day are less popular with the majority of travelers and you might find lower fares if you fly at that time. Likewise, certain times of year or season might offer lower fares. For example, you can be pretty confident travel will be brisk – and fares higher – if you fly over summer holiday weekends, including Memorial Day, Fourth of July and Labor Day.

This summer, save your gas money for necessity traveling and consider finding cheap flights online instead – you may just find the savings helps defray the rest of your vacation costs.