What happened

Shares of oil and gas royalty trust BP Prudhoe Bay (BPT -1.53%) are down 17% as of 11:45 a.m. EDT today. The likely impetus for today's drop was the Friday announcement of the trust's dividend payout for the quarter. 

pumpjacks at sunset.

Image source: Getty Images.

So what

If you were to look up BP Prudhoe Bay's dividend payouts over the past year, you would find that the trust paid out about $5.07 per share -- which, at today's stock price, makes for a rather fat yield of better than 18%.

I'm sure that there were a few people out there who saw that number and immediately assumed this stock was a steal.

The trouble is, BP Prudhoe Bay's dividend isn't a fixed amount. It is a royalty payment based on the price of a barrel of oil during the quarter and the amount that the operator of the field -- in this case, BP (BP -2.95%) -- extracts. During the fourth quarter, oil prices were considerably lower than what they were in the previous quarters. As a result, the royalty payment for the quarter was $0.33 per unit.

Brent Crude Oil Spot Price Chart

Brent Crude Oil Spot Price data by YCharts

Now what

It's hard to say precisely what happened to cause the stock to drop today, but since the dividend payment isn't due until April 22, some investors are probably exiting after seeing that paltry payout. 

That is the name of the game with royalty trusts, though, as their payouts are almost wholly dependent upon the price of oil and gas in the quarter. This most recent quarter wasn't a great one for investors, but with Brent oil prices sneaking up closer to $70 per barrel, chances are the next quarterly payout will be higher.