Surfactants may also cause problems at later stages of oil processing. In some cases, especially where the extracted crude is recovered in the presence of a great deal of water, the presence of surfactants produces emulsions or microemulsions that must be broken and the water separated before further processing can occur. Naturally present surface-active materials in the crude plus any added surfactants can produce surprisingly stable emulsion systems. The petroleum engineer dilemma: (1) surfactants are necessary for efficient extraction, (2) but their presence produces difficult problems in subsequent steps.