The booming shale oil industry has been borrowing to maintain its quick expansion, but energy exchange traded fund investors should not worry about rising rates cutting into growth.

Raymond James calculates that between 2006 and 2012, U.S. exploration and production companies tacked on almost $1 trillion in capital expenditures, compared to $670 billion in operating cash flows, the Wall Street Journal reports.

According to IHS data, the energy and production sector saw net debt per barrel rise 36% to over $39 last year from $28.84 in 2007 while cash flow was relatively flat.

The borrowing spree has helped energy companies expand, with the Market Vectors Unconventional Oil & Gas ETF (NYSEArca: FRAK) up 15.0% year-to-date. FRAK tracks the performance of the unconventional oil and gas market, including shale and oil sands. In comparison, the broader S&P 500 Energy Index is up 8.8% so far this year. [Oil ETFs to Tap into the Energy Industry]

Some critics may argue that oil exploration and producers could experience lower spending as the Federal Reserve moves closer to hiking near-zero rates.

However, investors shouldn’t be too worried about the effects of rising rates on the shale oil industry. Brian Gibbons at CreditSights points out that about 90% of the sector’s existing debt holds fixed interest rates, and the industry does not face demand to pay back or roll over debt. Gibbon said that nearly 60% of the $346 billion in outstanding debt does not mature until after 2020. High-yield issuers, though, could face constraints as debt-servicing costs rise.

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