An arrangement between a buyer and a supplier in which they agree to apportion benefits (such a reduced costs, or increased outputs) arising from particularly sound contract performance may be called:

Gainshare (or gainsharing) is a contractual mechanism in procurement where a buyer and supplier agree to share financial or operational benefits resulting from superior performance, innovation, or continuous improvement initiatives. Under a gainshare agreement, cost savings or performance gains achieved relative to an agreed baseline are apportioned between both parties according to a predetermined ratio. This arrangement aligns supplier incentives with buyer objectives, promoting collaborative working relationships and shared continuous improvement. Painshare, by contrast, involves sharing financial losses or performance failures.

Option A: Painshare is an arrangement where the buyer and supplier share financial risks, losses, or cost overruns resulting from underperformance or unforeseen issues.
Option B: Stocks and shares represent equity ownership units in a commercial entity, rather than a performance-benefit sharing agreement between procurement contracting partners.
Option C: Fair share is a general descriptive phrase referring to equitable division, not an established contractual framework for performance gain distribution.

- CIPS L3M1 Study Guide: Procurement and Supply Environments, Unit 3: Contractual Arrangements and Relationships, Section 3.2.

- Lysons, K. and Farrington, B. (2020) Purchasing and Supply Chain Management, 10th edn. Pearson Education, pp. 412–415.