Travelers expect—or at least hope for—fast, reliable cellular connections wherever they go. On the road. In the store. At the airport. On the plane. At the hotel. On the mountaintop.

The reality, though, is that solid cell service is a crap shoot. It’s here and there, but not everywhere.

Where travelers rely particularly heavily on smartphone connectivity is at the airport. A new study by RootMetrics ranking the cell service at the nation’s 50 largest airports shows just how hit-and-miss it can be.

The rankings are based on an average of the scores of available cellular-service providers (AT&T, Sprint, T-Mobile, and so on), weighted by the estimated percentage share held by each provider.

So, for instance, at Oakland Airport, which topped the list, download speeds exceeded 60 Mbps on the networks of AT&T, Sprint, and Verizon, with 99.9 percent reliability. At those speeds, travelers can binge-watch the latest Netflix hit while waiting to board their flights. At the other end of the spectrum, download speeds at Los Angeles International Airport averaged a pokey 2.8 Mbps on AT&T, and just 0.5 Mbps on Verizon. Those speeds are barely adequate for checking email or perusing Facebook.

The 10 airports with the best cell service:

1. Metropolitan Oakland
2. General Mitchell, Milwaukee
3. Southwest Florida, Fort Myers
4. John Wayne, Orange County
5. Logan International, Boston
6. Hartsfield-Jackson Atlanta
7. Indianapolis
8. Sacramento
9. Love Field, Dallas
10. Midway International, Chicago

And the bottom 10, worst first:

1. Los Angeles International
2. Austin-Bergstrom
3. Ft. Lauderdale, Hollywood
4. Philadelphia
5. William P. Hobby, Houston
6. Nashville International
7. Honolulu
8. Detroit Metropolitan
9. Louis Armstrong New Orleans
10. Seattle

Of course, using your cell provider’s connection isn’t the only option. In many cases, airports offer their own WiFi service. But airport WiFi tends to be slow, insecure, and expensive. Depending on the airport, it may or may not be a better alternative.

After 20 years working in the travel industry, and almost that long writing about it, Tim Winship knows a thing or two about travel. Follow him on Twitter @twinship.

This article first appeared on SmarterTravel.com, where Tim is Editor-at-Large.