The correct answer is C) The designated person in charge. During oil transfer operations, the designated person in charge (typically the person in charge of the transfer operation, such as the Tankerman or Cargo Officer) is responsible for ensuring that the posted transfer procedures are being followed. This is in accordance with Coast Guard regulations, which require the person in charge to oversee and verify the proper execution of the transfer procedures to maintain safety and prevent spills. The other options are incorrect because the tankerman, senior able seaman, and oiler are not specifically designated as the responsible party for verifying the transfer procedures, even though they may have other roles and responsibilities during the transfer operation.