Just yesterday I was looking at the woefully low share prices of Royal Bank of Scotland and Barclays and thinking how much they reminded me about BP and Vodafone when their share price struggled in recent years.

The similarities are very striking. They are all some of the biggest heavyweights in the FTSE 100, and yet at times they've become really unloved and hit ridiculously low levels.

Let me give you a quick bit of background.

BP went from over 700p to just over 500p in less than a year, before recovering to 640p (current price = 583p).

Vodafone dropped from 157p to around 108p, before staging a big recovery and currently stands at 196p.

In current times the major banks have all suffered similar drops due to the sub-prime crisis. Royal Bank of Scotland, for example, has fallen from 725p to under 400p, and although it's recovered slightly, still stands at a lowly 458p.

What I'm seeing now with these banks is exactly the same as what I was seeing when BP and Vodafone were hitting new lows.

The banks have become unloved amongst private investors, analysts are starting to issue sell notes, they're trading at ridiculously low PE ratios, and the forums are full of clowns saying you should short these companies as they're going bust. The people still holding onto huge losses are either holding desperately whilst calling for the CEO's head, or panic selling and driving the price down even further.

All of which happened with BP and Vodafone, and they subsequently bounced back strongly. The turning point seems to be when everyone is selling, and I've always maintained that the best time to buy quality companies is during their periods of weakness when investors start panic selling, and this is my current opinion of the major banks.

Of course there is still a major risk in the short-term because we still don't know how much the banks in the UK are exposed to sub-prime loans, but my own opinion is that it won't be as much as some of the doom and gloom merchants in the media are predicting.

There's also the fact that in the long-term the major banks should have more than enough resources to fully recover from this sub-prime mess, and coupled with the fact that their dividend payments are upwards of 7% in some cases, I feel they offer a good long-term buying opportunity.

I should point out that this is just my opinion, and I do personally own shares in Royal Bank of Scotland, but I do feel that in a few years time the major banks will recover from their current lows, like BP and Vodafone did, but of course until we know the full extent of the losses from the sub-prime crisis there is always a further downside risk in the short-term.