Russian gold miner Petropavlovsk (LSE: POG) has executed a remarkable recovery from its near-terminal debt problems of a year ago. Petropavlovsk’s latest results show that net debt fell by 34% to $610m last year, a significant achievement.

Although some of this reduction was achieved using cash from last year’s rights issue, the firm’s mines are now profitable again. Petropavlovsk’s cash cost of production was $749/oz. last year. With gold now trading at well over $1,200/oz., cash flow should be strong and net debt is expected to fall to $570m this year.

The group is now targeting expansion. It recently announced an acquisition and a joint venture to complete the firm’s postponed POX hub project. Both should add to production.

My biggest worry is that the firm’s debt problems may not be resolved. According to the firm’s latest results, Petropavlovsk expects to breach its lending covenants again in June if it can’t obtain a fresh covenant waiver before then.

If this hurdle can be overcome and debt continues to fall, then I believe the shares have the potential to double over the few years.

Will the oil recovery be enough?

A similar story might apply to North Sea oil firm Enquest (LSE: ENQ). Enquest has a challenging $1.2bn net debt burden on which repayments are due to start in 2017.

The firm’s cash flow currently benefits from a hedging programme. This covers about 60% of forecast 2016 production at an average of $68 per barrel. The problem is that Enquest doesn’t appear to have any hedging in place for 2017.

With oil currently trading at about $47 per barrel, cash flow could be very tight next year unless Enquest is able to secure a new hedging programme.

Indeed, City forecasts suggest that despite rising revenue from higher production, Enquest is likely to report an increased full-year loss in 2017. Unless the price of oil stages a very strong recovery — above $60, perhaps — then I think Enquest could find it difficult to meet its debt repayment schedule in 2017.

For this reason, I believe Enquest shares are too risky to buy at the moment.

Profits may soon be rising

Engineering firm Fenner (LSE: FENR) has been hit hard by the mining and oil downturns. But the group also has a medical division that’s doing well. Fenner’s management has worked hard to reduce the firm’s exposure to the commodity sector.

The group’s recent interim results suggested to me that the company may have reached a turning point. Although underlying operating profit was 48% lower than for the same period last year, operating cash flow was unchanged at £19m, thanks to a reduction in normal seasonal cash outflows.

While market conditions remain tricky, Fenner’s management believes that the firm’s production capacity is now better matched to lower demand levels.

The latest consensus forecasts suggest that the City agrees. Adjusted earnings are expected to rise from 7.7p per share this year, to 9.1p per share in 2017. The rebased dividend is expected to be stable at about 4p per share.

I think that there’s a reasonable chance Fenner’s shares could double to 300p over the next few years.

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Roland Head owns shares of Fenner. The Motley Fool UK has no position in any of the shares mentioned. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.