What: Last month was pretty rough for investors in Oil States International (OIS -4.02%) after crude prices took another tumble.

So what: The global oil benchmark price slumped 16% last month after resilient supplies continued to push crude oil inventory levels higher. That left the price of crude just north of $37 per barrel, which is below the break-even point of most new oil developments. The implication being that the slowdown in oil-field activity could continue to grow worse.

That would suggest that Oil States' business could continue to slow. Prior to the downturn, the company had been growing its offshore product EBITDA by a 13% compound annual rate since 2009. However, the company is poised to experience a year-over-year decline in that segment's EBITDA, which over the trailing 12 months is off $34 million from last year's level of $222 million. Even worse is its well-site services segment, which had been growing at a 19% compound annual growth rate. That segment's EBITDA, however, is down $147 million over the trailing 12 months from the $282 million it earned last year.

It's that well services segment in particular that could continue to weaken. Oil States has already seen the operating income margin from completion services fall from the mid-20s to the low single digits. The concern is that it could have a lot farther to fall, especially when some of its peers have seen their margins go negative. Rival Superior Energy Services (SPN), for example, has experienced a 57% year-over-year revenue decline in its onshore completion and services segment due to continued pricing pressure in all of its product lines as well as lower utilization levels. Because of that, Superior Energy Services' adjusted net income from operations in that segment was negative last quarter. Furthermore, Superior Energy Services' outlook is for these "trends to continue in the fourth quarter and into the next year" according to CEO David Dunlap, because the low oil price is having a deep impact on customers' ability to fund new wells.

Now what: Times are tough for oil-field services companies and could get even tougher given the continued drop in crude prices. This suggests that a lot more volatility could still be ahead for Oil States investors.