* Tullow already hit by bad news before oil price slump
* Bets against Premier Oil shares also rising
By Maiya Keidan and Shadia Nasralla
LONDON, March 11 (Reuters) - Short positions on Tullow Oil shares hit a more than 15-month high on Monday, data from industry tracker FIS' Astec Analytics showed, in a sign of investors growing pessimism over the company's prospects ahead of its 2019 results on Thursday.
Shares in Tullow have nosedived around 92% in the past six months on the back of weak output in Ghana, delays in East Africa, lower-than-hoped-for oil quality in Guyana and a dry well in Peru.
Short positions involve investors borrowing stock to bet the price will fall.
Tullow is cutting around a third of its workforce, seeking to sell stakes in some of its assets and hunting for a new chief executive.
Its shares, like those of other exploration and production-focused companies such as Premier Oil, have come under further pressure since Monday's oil price slump, the worst since 1991.
Brent crude oil brenchmark futures were trading just under $36 a barrel at 1136 GMT.
Tullow has around 60% of its 2020 production hedged at $57 a barrel and its free cash flow break-even point is $40 to $45 a barrel.
According to the data, 18.1% of Tullow shares available to be loaned were out on loan. The company declined to comment on the figures.
Hedge fund firms Citadel and Odey Asset Management held outstanding short positions in Tullow of 0.84% and 1.44%, respectively, according to filings with British regulator the FCA. They were not immediately available for comment.
British firms are obliged to report changes in short positions to the regulator once they surpass a threshold of 0.2% of a company's shares and must make them public once they hit over 0.5%.
Meanwhile, Premier, which is planning a $500 million capital hike to buy fields in the North Sea, has yet to decide with its shareholders and underwiters Royal Bank of Canada (RBC) and Jefferies on a price for the share issue.
Before this can happen, a judge will rule on planned delays to Premier's debt maturities in a hearing starting on March 17.
Shorts against Premier have also risen since the outbreak of the coronavirus in early January, with 73.1% of the available shares out on loan, according to the data.
Premier shares have fallen around 77% in the year-to-date to around 23 pence. (Editing by Mark Potter)