What is the primary reason an op-amp output might saturate when trying to amplify a signal?

When the desired amplified voltage exceeds the op‑amp’s supply rails, the device can no longer produce the required output and instead “clips” at the nearest rail voltage. This happens because the op‑amp’s output stage is limited to the supply voltage limits, so any signal that would drive it beyond those limits forces it to saturate. In practice, if you try to amplify a 1‑volt signal by a factor of ten with a ±5‑volt supply, the ideal output would be ±10 volts, which is impossible, so the output stalls at ±5 volts. The op‑amp therefore saturates at the rail rather than following the linear amplification. This is the main reason why an op‑amp output can saturate.