Spilled is favoured in American English as both the past tense and past participle. British English, as you may have suspected, prefers spilt, also for both.
Spill Verb Forms: Past Tense and Past Participle (V1 V2 V3) – EngDic
Spilled or Spilt – What's the Difference? - Writing Explained
How to Use Spilled vs. spilt Correctly
What's the Past Tense of Spill? Spilled vs Spilt
How much raw sewage is released into rivers and the sea, and what
How to Use Spilled vs. spilt Correctly
Spill V1 V2 V3 V4 V5 Base Form, Past Simple, Past Participle Form
Spill - Definition, Meaning & Synonyms
Past Tense of Spill, Past Participle of Spill, V1 V2 V3 V4 V5 Form
Global average oil spills per decade 2023
Largest Oil Spills Affecting U.S. Waters Since 1969