When machine-hours are used as an overhead cost-allocation base, the most likely cause of a favorable variable overhead spending variance is

A favorable variable overhead spending variance occurs when the actual costs are less than the standard costs. When machine-hours are used as an overhead cost-allocation base, the most likely cause of a favorable variance could be:

1. Efficient use of machinery: If the machines are used efficiently, they may require less maintenance, repairs, and energy, leading to lower costs.

2. Lower prices for overhead items: If the prices of overhead items such as utilities, supplies, or indirect labor are lower than expected, this could result in a favorable variance.

3. Less machine hours used: If fewer machine hours are used than expected, this could also result in a favorable variance as less overhead costs would be incurred.

4. Better quality materials: If the materials used are of better quality, this could result in less waste and fewer machine breakdowns, leading to lower overhead costs.

5. Improved technology or processes: If new technology or processes are implemented that increase efficiency, this could also lead to lower overhead costs.

Remember, a favorable variance is not always a good thing. It could indicate that the standards were set too high, or that there could be quality issues due to cost-cutting measures.