It’s time for our monthly look at how the long-only commodity ETFs are performing versus simply holding the December futures contract and rolling annually.

Crude oil climbed higher in August, while natural gas took a tumble and corn stayed fairly flat. ETF underperformance against the December futures contract widened for crude oil and natural gas, but narrowed slightly for corn.

Futures trading is complicated, presents a risk of loss, and isn’t for everyone – especially since past market performance doesn’t necessarily indicate future results – but given the numbers, we’re left scratching our heads. Ultimately, we prefer a commodities investment strategy that can benefit from both rising and falling prices (like managed futures). But if you’re going to adopt a long-only strategy… we’ve yet to receive a good answer to the question: why invest in an ETF when you can just roll December futures contracts annually?

Read ‘em and weep: