Consider the simple table of marginal abatement costs (MCA) given to the right.
If both firms are given credits to cover 50% of their current pollution, they must either reduce pollution by 50% or purchase credits. At 50% abatement, marginal cost for Firm 1 is 50 while for Firm 2 it is 110. Since it cost Firm 2 110 for the last unit of pollution reduced at 50%, if it can purchase credits for under 110 per unit it will be better off. Furthermore, since it only cost Firm 1 50 for the last unit it removed at 50%, if it can sell credits for more than 50 it will be better off.
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| Firm 1 % Abatement | MCA | Firm 2 % Abatement | MCA |
| 10 | 10 | 10 | 70 |
| 20 | 20 | 20 | 80 |
| 30 | 30 | 30 | 90 |
| 40 | 40 | 40 | 100 |
| 50 | 50 | 50 | 110 |
| 60 | 60 | 60 | 120 |
| 70 | 70 | 70 | 130 |
| 80 | 80 | 80 | 140 |
| 90 | 90 | 90 | 150 |
| 100 | 100 | 100 | 160 |