South Florida-based construction company MasTec (NYSE:MTZ) reported its third-quarter earnings  this evening, and investors should be fairly pleased with the results. The company earned an adjusted $0.56 per share on revenue of $1.31 billion, which meets Wall Street's expectations on the top line and narrowly edges past the $0.55 in adjusted EPS analysts had expected. On a GAAP basis, MasTec earned $0.53 per share. Both GAAP and adjusted EPS figures were largely unchanged from the year-ago quarter, which recorded $0.54 in GAAP EPS and $0.56 in adjusted EPS.

Let's take a look at how MasTec's top and bottom lines have changed over time, to get a better idea of where it's been and where it might be going:

Mtzrevenueq
Source: MasTec earnings reports.
Note: Q4 2014 data is based on full-year guidance, less already-reported results.

Mtzepsq
Source: MasTec earnings reports.
Note: Q4 2014 data is based on full-year guidance, less already-reported results.

As you can see, MasTec's top line has shown relatively steady growth, with all but one quarter since the start of 2011 showing year-over-year growth, but its bottom line has been a bit more problematic, even when you focus on non-GAAP results. None of MasTec's four quarters this year are likely to result in a year-over-year improvement in adjusted EPS, which is a major reversal of a trend that had produced double-digit EPS growth from the second quarter of 2012 through the end of 2013 (MasTec did not report adjusted EPS before this time). Things should look brighter next year, as you'll see when we cover MasTec's forward guidance, but one way to explain the weakness in MasTec's current bottom line is to look at where its revenue is coming from, and how profitable those sources are.

Mtzsegmentrevenueshareq
Source: MasTec earnings reports.

As you can see, MasTec's relationships with the petroleum and communications industries are clearly driving its results, with revenues from oil and gas companies nearly doubling from the start of 2012 (22.7% of all revenue) to the current quarter (42.6% of all revenue). However, scaling up its oil and gas operations has caused problems for MasTec's bottom line over the past few quarters -- although it now seems better able to manage its costs -- which has hindered its results as EBITDA margins from communications contracts have fallen in 2014:

Mtzsegmentebitdaq
Source: MasTec earnings reports.

So there is good news and bad news here, but MasTec's forward guidance seems to offer more good news than bad. Looking ahead, MasTec now expects roughly $4.6 billion in full-year revenue and roughly $1.55 in adjusted full-year EPS, and has also issued preliminary guidance for 2015 that calls for revenue to range from $5.2 billion to $5.4 billion, resulting in adjusted EPS in the range of $2.00 to $2.15.

Analysts had expected $4.5 billion in full-year revenue, and $1.56 in full-year EPS, so neither of these projections were out of the ordinary. However, Wall Street may be disappointed that MasTec failed to reach its projection for $2.18 in 2015 EPS even at the high end of its guidance range. Still, the midpoint of MasTec's 2015 guidance implies a forward P/E of just 12.7, based on adjusted earnings. All in all, this was a solid report, though perhaps not as impressive as Wall Street had hoped for. Foolish investors, of course, learn to ignore Wall Street and focus on the long term, and the long term looks to produce more of the positive earnings momentum that investors have been waiting for.

Alex Planes owns shares of MasTec. Follow him on Twitter @TMFBiggles or connect with him on LinkedIn for more insight into investing, markets, economic history, and cutting-edge technology.

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