SACRAMENTO - You may not be getting what you pay for when you exchange your empty propane tank for a full one. Now one state agency is launching a full scale investigation into what's called "short-filling" -- when a propane tank isn't filled to capacity.

The inquiry is in response to several complaints that these tanks are coming up short. Propane customers across America are hissing mad over the idea propane companies are giving them less fuel for the money. Last year when gas prices rose, so did the price of propane. To off-set those costs propane companies chose to give consumers less propane rather than raise prices. But as propane prices fell back down, the tanks weren't filing back up.

According to Sacramento County's Weights and Measures Department, propane sales and containers are monitored on a complaint basis. We asked a local Home Depot whether or not they test their tanks capacity which are brought in by different companies. They use Amerigas, and say they've never had a complaint from a customer that their tank wasn't filled.

An empty propane tank empty can be anywhere from 16 to 18 lbs; filled up, it should weight almost double that. So how can you tell if you've been short-filled by a couple pounds?

According to the County of Sacramento Director of Weights and Measures, "You can test it on a bathroom scale, but most bathroom scales are not that accurate, but that's about all a consumer can probably do." We tested that method with our own empty cylinder and found a difference of about 15 pounds, meaning it was filled to legal capacity.

Now, if you don't want to deal with the hassle of wondering whether you're getting your fill, you can take them to places where they refill right in front of you.