Historical generalization in petroleum geology: older crude petroleum is often described as lighter and “better.” Based on this generalization, indicate which outcomes are expected for older crude—greater share of distillates and reduced tar formation—choosing the most inclusive option.

Introduction / Context:
Across many basins, crude oils undergo long-term geologic maturation. In broad textbook generalizations, “older” crudes are often portrayed as lighter, with higher API gravity, yielding larger fractions of distillates and less heavy residue or tar. While real-world exceptions exist due to source rock type, migration, biodegradation, and thermal history, this question asks you to apply the conventional generalization used in many introductory refinery and petroleum geology texts.

Given Data / Assumptions:

• “Older” refers to more thermally mature oils in a conventional narrative.
• Comparison is qualitative: light vs heavy, distillates vs tar.
• We adopt the standard simplified teaching model.

Concept / Approach:
With increasing thermal maturity, kerogen cracking produces more oil and gas; secondary cracking can reduce average molecular weight, trending oils toward lighter compositions that distill at lower temperatures. Such oils typically provide higher proportions of light and middle distillates (naphtha, kerosene, diesel) and less residual fraction, hence “less tar.” This narrative underpins the assertion that older crude is “light and better,” from a fuels refining perspective that values higher distillate yields.

Step-by-Step Solution:

Verification / Alternative check:
Crude assay trends and basin maturity maps often show lighter, sweeter crudes in more mature settings; nevertheless, biodegradation or heavy source rocks can create exceptions.

Why Other Options Are Wrong:

Common Pitfalls:
Treating the rule as absolute; exceptions occur, but the question relies on the standard textbook generalization.

Final Answer:
All (a), (b) and (c)