| Schedule of Net Periodic Benefit Costs |
The components of Southwest Gas' net periodic benefit cost for its QRP, SERP, and PBOP for the three and six months ended June 30, 2026 and 2025 are presented in the following tables. | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Three Months Ended June 30, | | 2026 | | 2025 | | (Thousands of dollars) | QRP | | SERP | | PBOP | | QRP | | SERP | | PBOP | | Service cost | $ | 6,467 | | | $ | 52 | | | $ | 299 | | | $ | 6,099 | | | $ | 58 | | | $ | 292 | | | Interest cost | 16,726 | | | 589 | | | 835 | | | 16,397 | | | 596 | | | 857 | | | Expected return on plan assets | (22,221) | | | — | | | (694) | | | (22,581) | | | — | | | (624) | | | Amortization of prior service costs | — | | | — | | | 44 | | | — | | | — | | | 44 | | Amortization of net actuarial loss (gain) | 2,295 | | | 334 | | | (103) | | | 752 | | | 270 | | | (79) | | | Net periodic benefit cost | $ | 3,267 | | | $ | 975 | | | $ | 381 | | | $ | 667 | | | $ | 924 | | | $ | 490 | | | | | | | | | | | | | | | Six Months Ended June 30, | | 2026 | | 2025 | | (Thousands of dollars) | QRP | | SERP | | PBOP | | QRP | | SERP | | PBOP | | Service cost | $ | 12,934 | | | $ | 104 | | | $ | 598 | | | $ | 12,197 | | | $ | 116 | | | $ | 584 | | | Interest cost | 33,452 | | | 1,178 | | | 1,670 | | | 32,794 | | | 1,192 | | | 1,713 | | | Expected return on plan assets | (44,442) | | | — | | | (1,388) | | | (45,163) | | | — | | | (1,248) | | | Amortization of prior service costs | — | | | — | | | 88 | | | — | | | — | | | 88 | | Amortization of net actuarial loss (gain) | 4,590 | | | 668 | | | (206) | | | 1,504 | | | 540 | | | (157) | | | Net periodic benefit cost | $ | 6,534 | | | $ | 1,950 | | | $ | 762 | | | $ | 1,332 | | | $ | 1,848 | | | $ | 980 | |
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