Net flows to a major exchange-traded fund covering the energy sector rebounded in September as oil prices rallied in tandem with investors' confidence.

SSGA's Energy Select Sector SPDR Fund led the dozen funds tracked by S&P Global Market Intelligence with $586 million in net inflows after $393 million in net outflows in August. Overall, the funds reported $517 million in net inflows in September as West Texas Intermediate crude oil rose 9.4% to settle at $51.67 on the last day of the month.

According to Todd Rosenbluth, director of mutual funds and ETF research at CFRA, the recent flows to the Energy Select Sector SPDR Fund, which has about $14.6 billion under management, indicated that investor sentiment toward the energy industry at large is improving. "[There] seems to be real demand from investors with optimism for large energy exposure," he said in an email. "With U.S. equities [having] continued to move higher in the second half of year, some investors have started to look at underperformers."

The fund itself has significant exposure to the exploration and production sector, with top two holdings Exxon Mobil Corp. and Chevron Corp. accounting for over 40% of its total portfolio as of Oct. 6.

The 11 midstream-focused ETFs tracked by S&P Global Market Intelligence saw net inflows increase by over $100 million, to $435 million, in September. Even though the midstream sector's Alerian Master Limited Partnership Index increased by just 0.7% for the month, net flows to the Alerian MLP ETF based on the index were nearly $326 million September, up from $198 million in August.

September was also marked by a flurry of capital markets activity and a series of initial public offerings, indicating to some industry observers that investors are ready for MLPs to start growing again.