It has been a week of steep drops for some emerging-market stocks, but Johannesburg-traded Sasol has out-plunged its peers, battered by the crash in oil prices and concern among investors of a potential looming rights offer as it grapples with a debt burden of about R129bn.

Shares in the synthetic fuel and chemicals producer, SA’s biggest company by sales, have lost more than 72% since the week started, the most among the 1,401 members of the MSCI Emerging Markets Index, which is down 5.6%.

The latest slump has dragged the stock to levels last seen in early 2001. Sasol delayed an investor call scheduled for Tuesday until March 17, noting that its oil-price exposure for the rest of the fiscal year is not hedged.

While the company had assumed oil would stay in a range of $50 to $70 a barrel, Brent crude traded just above $36 on Wednesday. The stock closed 26.44% to R52.72, valuing the company at R33bn. At its highest recorded price, which came in June 2014, it had a market cap of more than R400bn.

The yield on its $750m (R12.112bn) of notes due in 2028 climbed for a sixth day to a record 6.93%. Sasol’s 0.6% weighting in the JSE’s benchmark index has limited its effect on the overall market. Among emerging markets, Poland’s WIG 20, Russia’s dollar-denominated RTS index and Saudi Arabia’s Tadawul all share index have been the worst performers this week, falling at least 12%, while SA’s gauge has dropped about 5.7%.