In the last three months, shares in BHP Billiton Limited (ASX: BHP) have risen by 21%. This indicates that investor sentiment is on the up alongside commodity prices like iron ore.

Many investors may therefore wonder if now is the perfect time to buy BHP, since the worst of the commodity price falls may be over and yet the company’s shares could still offer good value for money. After all, they are still down by 56% in the last five years.

Undoubtedly, BHP is a very appealing resources stock. Unlike resources peers such as Rio Tinto Limited (ASX: RIO) and Woodside Petroleum Limited (ASX: WPL), BHP is highly diversified.

While Rio Tinto relies on iron ore for 87% of its underlying earnings and Woodside is a pure play oil and gas company, BHP produces oil, and mines iron ore, copper and uranium. This provides it with a breadth of operations (even after its split), which few ASX-listed resources companies can match. This means that BHP could be seen as a neat way to gain exposure to a wide range of commodities for most investors. This is not available to the same extent with the likes of Rio Tinto and Woodside.

Further, BHP has strong finances which should allow it to survive if a major commodities downturn resurfaces. For example, it has a debt to equity ratio of just 44% and was able to cover interest payments on its debt 12.4 times with operating profit last year.

Additionally, BHP has the cash flow to support major reinvestment for future growth. Its net operating cash flow has averaged USD$21.6 billion over the last three years and the company has spent an average of 75% of that figure on capex during the same period. This shows that while BHP has mothballed a number of projects, it is still investing heavily for its long-term growth prospects (as well as maintaining assets which are currently producing) and this bodes well for its long-term profitability.

On this front, BHP’s strategy also makes sense in my view. It has raised production significantly in the face of lower commodity prices. For example, iron ore and metallurgical coal production rose by 14% and 13% respectively in 2015.

This benefits not only the company’s bottom line, but also its competitive position relative to peers. That’s because it helps to maintain BHP’s market share and this should enable it to benefit to a greater extent than it otherwise would as and when commodity prices fully recover.

In this regard, the future remains  uncertain. Commodity prices could rise, fall or trade in a narrow range. Therefore, a wide margin of safety is a must-have for investors in BHP. Its shares currently trade on a P/B ratio of 1.23 versus 1.15 for the wider materials sector.

Therefore, while BHP has the right strategy in my view and its diversification and financial strength make it a leading resources company to own, today does not seem to be a once-in-a-lifetime opportunity to buy it. Sure, it may be worth holding as part of a diversified portfolio, but there may be better (and cheaper) opportunities to buy it over the medium term.

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Motley Fool contributor Robert Stephens has no position in any stocks mentioned. 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.