It's time to think about that summer vacation.

Welcome to the crowded skies. Many flights are already full or oversold. Even more planes will be packed to capacity this summer.

I flew back last night from Minneapolis where I spent some time with one of the country's top travel experts, Terry Trippler of tripplertravel.com.

I feel I've got to tell you, I felt like a sardine in the back of that 737-300. I think there was one empty seat on the plane.

As hard as I tried prior to takeoff, I could not get an aisle seat or an exit row seat. And I was willing to pay for the upgrade!

Flying really isn't fun anymore. The planes are packed and it's only going to get worse when summer arrives.

"It's going to be a love thy neighbor summer, because you're going to be sitting beside one on the plane," Trippler said.

"We're going to have a lot of planes 100-percent full. Summer travel domestically looks very good. And internationally, it's amazing.

"But it's holding very, very well. Even considering how the Euro is killing the U.S. dollar, Americans are still going. The bottom line is Americans just won't stay home," he said.

If there's any sort of problem this summer - weather delay or mechanical problem, it's going to screw up the system for days.

A plane booked for 150 passengers might cancel. And chances are there might be one or two empty seats on the next flight. So where do you put the rest of the people?

Trippler says if you're going to fly, you need to plan for the worst; you can't cut it too close anymore.

"If you have to be at work on Monday, come home on Sunday. If you have to be at that groom's dinner on Friday night, go on Wednesday night," he said.

Trippler expects the biggest price hikes on flights to secondary cities such as Omaha, Pittsburgh and Oklahoma City.

Higher prices are also expected between hub cities with no competition from low-cost carriers. That would include routes such as Seattle to Denver, Seattle to Minneapolis-St.Paul and Seattle to Detroit.

The one bright spot for those headed to Europe could be the airfare. Thanks to a new open skies agreement, airlines can fly between the U.S. and Europe without getting approval from either government; they just need a place to park the plane.

What this means, Trippler says, is more seats to Europe, which should help keep a lid on prices.

What about people who can't make up their mind? Should they book now for summer travel or wait?

"You book now," Trippler said. "Buy now, buy now. Fuel is going up, continually going up. Airfares are going up. They're not going to drop the prices.

"If you know where and when you want to go this summer. Buy it. If you know where and when you want to go on Thanksgiving. Buy it," he said.

I asked Trippler about the situation I ran into on my way to Minneapolis. I flew Northwest Airlines and tried to pay the $25 extra fee for an aisle seat.

"We're going to see much more of that. We're probably going to see just about every airline doing something like that," he said.

To withstand rising fuel prices without driving too many customers away, the airlines need to find creative ways to make money. Trippler says that's why travelers should expect to see more a-la-carte pricing.

"When you get a ticket, you get a ticket from point A to point B. If you want anything else, you can pay for it. It's not so much you get what you pay for. It's more of 'whatever you want, we're going to charge you.'

"It has become a tremendous revenue source for the airlines. United Airlines now has their Premier Plus coach seats (which) charge a little more (and) you have more leg room. You're going to see more and more of that.

"When you think about it, you pay more to have a better seat at a ballgame, you pay more to have a better seat at a concert, why shouldn't you be willing to pay more and I'm willing to pay to have a better seat on a plane?" Trippler said.

A lot of people won't agree with that logic but like it or not, that's the way it is. If you want something, the airlines are going to charge you for it. Trippler says he wouldn't be surprised if before too long, passengers will have to pay $1 for a can of soda in the air.