Final answer:
Following the deal with Vanderbilt, Rockefeller encountered transportation challenges, which he addressed through vertical integration, investing in railroads and pipelines to maintain control over oil supply chains.
Step-by-step explanation:
After making a deal with Vanderbilt, Rockefeller faced transportation issues. Seeking further control of his business, he engaged in vertical integration, handling all aspects of production from the creation of raw materials to the delivery of the final product. However, in the beginning, his expansion created transportation challenges that he needed to address, as he aimed for control over not just refining but also moving and marketing his oil products. This quest to dominate transportation led him to also invest in railroad companies and develop a vast pipeline network to ensure efficient delivery and dominance over competitors.