If your gas oven is giving off an unpleasant odour, a number of different things could be causing the problem. The source of the odour can depend on a number of factors, including the age of your home, the placement of your oven and the age of the oven itself.
One of the most common culprits off oven odours is food residue. While an item is cooking, a piece of food or a sauce spills over the side of a container and causes your oven to smell. If you don't use your oven very often, the food may begin to rot inside your oven. If a burnt smell occurs while you're cooking, your oven is probably burning off food that has dropped.
If your gas oven was just installed and there is a chemical odour when you turn it on, this most likely is caused by the appliance off-gassing. Ovens, like other appliances, often have certain chemical residue still on them. Many oven instruction manuals tell you to start up your oven and cook off this substance before you actually use the oven. Open all the windows in the room to help the smell dissipate.
If your oven is emitting a chemical smell, try to remember the last time you used oven cleaner. If it's been recent, this mostly likely is the cause of the odour. Depending on the type of oven cleaner you use, a residue can be left on the inside of your oven. When you start your oven again, the residue burns off, causing the odour.
The smell of something decomposing is never pleasant, and it's even less so when it's coming from your oven. If your oven starts to smell like something that was once living is rotting nearby, it's probably time to move your oven and check behind it. Because of the warmth, mice often like to make their homes behind ovens and a dead mouse may start to decompose, causing the smell. Mice may also defecate and urinate behind your oven, leaving an unpleasant and unsanitary odour.
If you ever smell gas around your gas oven for more than a few seconds, turn off the gas to your oven. The smell of gas around your oven could mean you have a gas leak. If you're familiar with gas issues, you can check the line yourself or call in a professional. If the gas smell only occurs for a couple of seconds when you light the burner or pilot, there's rarely a reason to worry as this is common and expected.