Source: Mistras Group.

Some of the best returns come from businesses that fly under the radar of just about every mainstream investor out there. Mistras Group (NYSE:MG) is one such stock, with its focus being to help its industrial customers test their equipment and systems to ensure that they perform as efficiently and effectively as possible. Mistras' innovative methods of testing machinery while it's still running at its facility represent a huge step forward from previous testing methods that required substantial off-time, and its software helps clients monitor and track their maintenance needs. Coming into Wednesday afternoon's release of its fiscal second-quarter results, Mistras investors had hoped to see substantial sales growth, and the company delivered everything most shareholders wanted and then some. Let's take a closer look at Mistras Group's quarterly results to see what drove the company's growth and what lies ahead for the company in 2015.

How Mistras crushed expectations this quarter

Mistras Group touted its record results for the quarter, with growth rates coming in far greater than most investors had expected. Overall, revenue soared 32% from the year-ago quarter to $206.9 million, a growth rate that nearly doubled consensus estimates. The company also defied pessimistic investors by posting gains in earnings per share, with the quarter's $0.35 per share up nearly 10% from year-ago figures. Even after adjusting for $0.02 per share in acquisition-related gains, Mistras easily topped the $0.26 per share that Wall Street analysts expected to see.

Looking more closely at its results, Mistras Group's revenue growth came from a balanced combination of acquisitions and organic sales gains, with buyouts accounting for about 60% of the company's overall increase in revenue for the quarter. Yet declines in gross profit margins from year-ago levels weighed somewhat on profitability, with Mistras blaming investments in Canada's oil sands as holding back higher-margin growth.

Source: Mistras Group.

Moreover, results from Mistras Group's various segments were mixed. The key Services segment posted huge success, with 48% gains in revenue driven both by organic growth and by acquisitions. Yet the International segment saw a 5% drop in sales, and Mistras' Products and Systems business suffered an even larger 13% decline in revenue.

Investors celebrated Mistras Group's results, sending the company's stock up more than 7% in after-hours trading within the first 30 minutes after the announcement. By beating expectations so squarely, Mistras inspired plenty of confidence that it can keep up its growth momentum.

Will Mistras Group keep up its pace?

Another reason why Mistras shares climbed likely came from its upbeat views about the remainder of its 2015 fiscal year. The company boosted its revenue growth estimates for the full year to a range of 16% to 19% over 2014, expecting between $720 million and $740 million in sales. Moreover, Mistras believes that its adjusted operating earnings will hit the high end of its previous guidance range, making gains of as much as 20% possible.

CEO Sotirios Vahaviolos. Source: Mistras Group.

Yet the upheaval in the oil market has been a concern for some Mistras investors. Company executives touted the growth potential from its recent acquisitions and growth efforts in the energy sector. As CEO Sotirios Vahaviolos said, Mistras' buyout of the Nacher Corporation "has gotten off to a fast start, helping to propel our acquisition-related revenue growth, and we remain optimistic about our efforts in the Canadian oil sands for the second half of the fiscal year." Still, with energy companies likely to have to look for ways to cut expenses if the dramatic plunge in oil prices lasts well into 2015, some fear that Mistras Group could see future pressure to the extent that it can't turn to other industries for potential growth.

Looking ahead, investors will want to watch closely to see how Mistras Group's energy customers react to changing conditions in the energy markets. Clearly, short-term traders have sent the stock upward based on the expectation that Mistras isn't too vulnerable to falling oil, and even if clients cut their future capital expenditures, it'll be tough for them to stop paying maintenance costs on their existing equipment. As long as its clients have the money to do regular maintenance, Mistras should have plenty of opportunity to make good on its growth promise.