May 14 (Reuters) - ONEOK Inc (OKE.N) agreed on Sunday to buy U.S. pipeline operator Magellan Midstream Partners (MMP.N) in a cash-and-stock deal valued at about $18.8 billion including debt, bringing natural gas-focused ONEOK into transporting refined products and oil. The deal will give ONEOK, until now a transporter of natural gas liquids and natural gas, access to Magellan's refined products and crude oil transportation business. The combined company will have 44% of its business in NGLs, and 21% in refined products, according to a presentation. The deal comes as U.S. natural gas prices have struggled this year because of oversupply concerns. Crude prices have traded off in 2023 on potential recession fears, although not as badly has natural gas.

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