What is proposed is the use of a water-soluble hydrophobically associating copolymer as an additive in the development, exploitation and completion of underground mineral oil and natural gas deposits and in deep drillings, wherein the copolymer comprises (a) at least one monoethylenically unsaturated monomer (a) selected from H2C═C(R1)—R4—O—(—CH2—CH2—O—)k—(—CH2—CH(R3)—O—)l—R5   (I), and/or H2C═C(R1)—O—(—CH2—CH2—O—)k—R2   (II), and (b) at least one monoethylenically unsaturated, hydrophilic monomer (b) different from monomer (a),wherein the copolymer is obtainable through copolymerization of the monomers (a) and (b) in the presence of at least one surfactant (c).