1. **State the problem:** We need to find the mass in kilograms of one barrel of oil carried by a supertanker. 2. **Given data:** - Mass of supertanker when full: 509.5 Mt (megatonnes) - Mass of supertanker when empty: 67.6 Mt - Number of barrels of oil when full: 3,166,353 barrels 3. **Step 1: Calculate the mass of the oil alone.** The mass of the oil is the difference between the full and empty mass of the supertanker: $$\text{Mass of oil} = 509.5 - 67.6 = 441.9 \text{ Mt}$$ 4. **Step 2: Convert megatonnes to kilograms.** 1 megatonne (Mt) = $10^6$ tonnes = $10^9$ kilograms. So, $$441.9 \text{ Mt} = 441.9 \times 10^9 \text{ kg} = 4.419 \times 10^{11} \text{ kg}$$ 5. **Step 3: Calculate the mass of one barrel of oil.** Divide the total mass of oil by the number of barrels: $$\text{Mass per barrel} = \frac{4.419 \times 10^{11}}{3,166,353}$$ 6. **Step 4: Perform the division:** $$\text{Mass per barrel} \approx 139,556.7 \text{ kg}$$ 7. **Step 5: Round to the nearest whole number:** $$\boxed{139557 \text{ kg}}$$ **Answer:** The mass of one barrel of oil is approximately 139,557 kilograms.