Australian shares fell back into negative territory today after a strong start to the week, with the S&P/ASX 200 (INDEXASX: ^AXJO) (ASX: XJO) index losing 1.3% to 4,938 points.

These four shares fell significantly further however, and here’s why:

Senex Energy Ltd (ASX: SXY) lost 7% to $0.14 today, despite a 2% rise in the value of crude oil. Although Senex remains a high risk investment as a result of its small size and exposure to volatile oil prices, the company has over 70% of its market cap in cash and carries no debt, putting it in a healthier financial position than many competitors.

While investors should expect the cash to dwindle as investments are made in commercialising its Surat Basin gas resources. Senex has a 20-year gas sales agreement with the Gladstone LNG plant, operated by Santos Ltd (ASX: STO).

Worleyparsons Ltd (ASX: WOR) shares fell 8.3% to $3.42, taking their loss to around 40% since the start of December 2015 – this despite announcing several new contracts in December. Short selling could be partly responsible for the fall, as disclosure notices from Credit Suisse show that CS has been dealing the shares under security lending agreements.

Mining services contractors like Worleyparsons continue to face a highly-competitive operating environment, as lower commodity prices cause companies to slash their capital expenditure budgets (reducing the available pool of work). Investors should do their research before making a purchase.

GUD Holdings Limited (ASX: GUD) didn’t have a very ‘gud’ day today, as shares crashed 10.6% to $7.06 after the release of its half-yearly report – which delivered a 63% fall in profit before tax as a result of $18.5m in write-downs. Revenue rose 20%, mostly due to acquisitions, while underlying profit (excluding write-downs) rose 17%. Although several segments grew, GUD also struggled to reduce costs in other areas like its Sunbeam and Dexion businesses.

An estimated 6% full-year dividend (at today’s prices) might be enough to get the bargain hunters looking more closely at the company, however.

Ten Network Holdings Limited (ASX: TEN) plunged 14% to $1.29, erasing much of the ground gained yesterday when shares recommenced trading on a T+3 (i.e., normal terms) rather than a deferred settlement basis. Some of the plunge is possibly due to shareholder fears the company is losing ground with its viewers after the X-Files reboot was delayed for a week. This leaves the show vulnerable to piracy and thus could reduce the potential size of the tv audience.

Ten shares have lost 90% of their value in the past five years.

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Motley Fool contributor Sean O'Neill owns shares of Senex Energy Limited. Unless otherwise noted, the author does not have a position in any stocks mentioned by the author in the comments below. The Motley Fool Australia has no position in any of the stocks mentioned. 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.