Shares of BHP Billiton Limited (ASX: BHP) have continued to rally today, lifting another 3.7% to $21.10. It’s the first time the shares have traded above $21 since November 2015, and they have now risen an incredible 33.7% in the last fortnight.

Indeed, BHP Billiton has proven many of its doubters wrong in recent weeks. Many individuals (myself included!) believed it was destined to continue falling as a result of plunging commodity prices, with some analysts even suggesting it would fall to just $10 a share, or perhaps even lower!

Instead, the shares hit a low of $14.06 on 21 January, and have barely looked back in the time since. Notably, Santos Ltd (ASX: STO) and Rio Tinto Limited (ASX: RIO) shares have also risen 79.8% and 37.9% in that time, while Fortescue Metals Group Limited (ASX: FMG) is up an impressive 145.6%.

Six-month price chart; Source: ASX

Six-month price chart; Source: ASX

These gains are largely due to the sharp recovery in oil prices since around that time, with West Texas Intermediate crude oil now fetching just under US$44 a barrel. Meanwhile, iron ore prices have also surged to nearly US$65 a tonne from a low around US$38 a tonne in December last year.

Iron ore and oil are BHP’s two most important commodities, so it comes as no surprise that the shares have bounced as a result. What has come as a surprise, however, is the magnitude by which they have recovered.

Missing out on such an impressive gain – particularly from a company like BHP – can be painful to think about too much, and many investors will be kicking themselves for not buying back in January or February.

However, the truth is that it is impossible to consistently predict the movements of commodity prices with any accuracy and, although iron ore and oil have both risen strongly in recent weeks, there is no guarantee they will remain that way.

Many analysts expect that iron ore will retreat again in the second-half of the year, while oil prices could also remain somewhat volatile from here.

BHP’s share price could have further to rise, but it does remain a risky bet. If commodity prices do take another tumble, BHP’s shares could certainly feel the weight of that, hurting anyone who buys in today. Of course, that isn’t to say they will fall, but investors should weigh up the pros and cons of holding BHP’s shares at today’s price levels.

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Motley Fool contributor Ryan Newman 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.