It's been an ugly year for the energy sector.

Year to date, the Energy Select Sector SPDR ETF (XLE) - Get Energy Select Sector SPDR Fund Report , a popular proxy for the energy sector as a whole, has shed about 10% of its market value. That's massive underperformance vs. the S&P 500, which has been on a double-digit tear to the upside over the same time frame. Without question, energy stocks have been the worst-performing sector in 2017.

And that awful performance is creating an awfully good opportunity as energy prices get shaken alive this fall.

Case in point: Exxon Mobil Corp. (XOM) - Get Exxon Mobil Corporation Report . Exxon has more or less mirrored its sector peers in 2017, down about 10% since the start of the year. That selloff has had the side effect of boosting Exxon's dividend yield -- Exxon currently hands out a 77-cent quarterly dividend that adds up to a 3.8% yield at current price levels.

So there's good reason for Exxon Mobil to be on income-seekers' radar right now.

More importantly, the price action is finally coming around as well, putting Exxon on the precipice of its first technical buy signal of 2017. To figure out when to pull the trigger on the Exxon trade, we're turning to the chart for a technical look:

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Exxon started the year with a sharp selloff, and it's spent most of the intervening months tracking sideways ever since. That sideways grind has actually been setting up the springboard that could send shares of this $344 billion energy giant higher.

The pattern in play right now is a rounding bottom, a bullish reversal setup that looks exactly like it sounds. The rounding bottom signals a gradual shift in control of shares from sellers to buyers, and it triggers with a push through the resistance level that's acted like a price ceiling for shares of Exxon all year long: $82.50.

Simply put, if Exxon can muster the strength to break through $82.50, we've got a clear-cut buy signal in this energy stock, and room to run up to prior highs at $90.

What makes that $82.50 level so important for this stock? It all boils down to buyers and sellers.

The $82.50 resistance level is a price where there has been an excess of supply of shares; in other words, it's a spot where sellers have previously been more eager to step in and take gains than buyers have been to buy. That's what makes a breakout above $82.50 so significant -- the move means that buyers are finally strong enough to absorb all of the excess supply above that price level.

That's good reason to wait for Exxon Mobil to push above that $82.50 price ceiling before you pull the trigger on this trade. It's our green light that buyers are back in control of the price action.

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This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.