Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of natural gas fueling company Clean Energy Fuels (Nasdaq: CLNE) fell 10% today, a day after the company announced earnings.

So what: Gallons delivered rose 23% from a year ago to 43.7 million gallons and adjusted loss per share of $0.16 was a penny better than expected. But revenue of $73.6 million fell short of expectations and the worry is that uptake of the company's product isn't going as quickly as expected.

Now what: The big question for Clean Energy Fuels has been how fast a move to natural gas fuel can take place. For now, it isn't going as quickly as expected and investors are fretting about the growth rate. On the positive side, the company did swing to positive adjusted EBITDA, and even if it's not as fast as expected, revenue is still growing. I'm cautious about the discount today and think shares may have further to fall. Until the company has some real momentum on the bottom line, I'll stick to the sidelines.

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