The S&P/ASX 200 (Index: ^AXJO) (ASX: XJO) has continued its good run and is getting ever closer to retracing its Brexit declines in full. So far today the index is up a solid 0.5% to 5,259 points.

There have been four shares in particular that have been doing a lot of the heavy lifting today. Here’s why they are soaring:

Aconex Ltd (ASX: ACX) shares are up over 9% to $7.65 following news that the growing software-as-a-service company has signed a new four-year enterprise agreement with US-based energy behemoth ExxonMobil. The new agreement means that all ExxonMobil companies and affiliates will have access to Aconex’s popular collaboration platform. Aconex’s management has called it “a strategic win with significant implications for us in the oil and gas industry.” Although its shares trade on an exorbitant earnings multiple, I believe the incredible growth prospects make them worth every bit of it.

Aconex shareholders will be delighted to learn that its share price is up over 47% this year.

Hansen Technologies Limited (ASX: HSN) shares are rocketing higher by over 9% to $3.71. Today’s gain is due to the announcement that it has acquired US-based energy billing company PPL Solutions. The purchase price is estimated to be 4x PPL Solutions’s EBITDA and will be paid for out of Hansen’s cash reserves. I believe this is good use of the billing services provider’s cash and expect it to add value for investors.

Hansen Technologies’ share price is up 37% in the last 12 months.

St Barbara Ltd (ASX: SBM) shares have rebounded strongly after recent declines with a 9% rise to $3.22. Just yesterday it looked as though gold miners were falling out of favour with investors now that markets were moving on from the post-Brexit turmoil. But St Barbara and industry peers Newcrest Mining Limited (ASX: NCM) and Resolute Mining Limited (ASX: RSG) have all put on strong gains today despite only a modest gain in the gold price.

St Barbara’s shares have rocketed by over 125% so far in 2016.

Whitehaven Coal Ltd (ASX: WHC) shares have gained 6% to $1.14 despite no news out of the company. Today’s gain could be related to reports in Mining Weekly that Fitch Group’s research firm BMI has raised its thermal coal price forecasts to $53 per tonne in 2016 and $57 per tonne in 2017. This is an increase from $51 per tonne and $52 per tonne, respectively. The forecast for an increase in coal prices has been put down to a larger-than-expected contraction in global mine output.

Whitehaven Coal’s share price has now risen by a massive 75% in the last three months.

Finally, if you've missed out on a lot of these strong gains today then i would recommend checking that you're not holding one of these three rotten shares in your portfolio. They could be holding your portfolio back from reaching its full potential.

3 Rotten Shares to Sell, and 1 to Buy Today

After a double-digit rally for the ASX since 2016 lows, investors should be on high alert. You'll find a full rundown below of 3 shares we think you should avoid today plus one top pick worth buying, even if the market turns south and the RBA keeps rates at an "emergency low." Simply click here to uncover these stocks.

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Motley Fool contributor James Mickleboro has no position in any stocks mentioned. The Motley Fool Australia owns shares of Hansen Technologies. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy. This article contains general investment advice only (under AFSL 400691). Authorised by Bruce Jackson.