All three agencies meet the same WRSTC (World Recreational Scuba Training Council) standards. Differences are marketing, not safety.
PADI (Professional Association of Diving Instructors): - Most globally recognized — ask any random dive shop and they'll know PADI - Brand premium: courses cost ฿11,000–฿14,000 in Thailand - Strong in: Phuket, Similan, Koh Samui - Best if: you plan to dive worldwide and want maximum brand recognition
SSI (Scuba Schools International): - Equally valid, owned by Mares dive equipment - 15–25% cheaper than PADI in Thailand - Strong in: Koh Tao, Koh Lanta, Phi Phi - Best if: budget-conscious, doing Thailand-only trip
NAUI — uncommon in Thailand, mainly US military and Japan RAID, CMAS, BSAC — exist but rare
Practical advice: - Pick instructor over agency: a great SSI instructor > mediocre PADI instructor - Read individual dive shop reviews (Verified Thai aggregates these) - Same exact skills are taught: 4 confined water + 4 open water dives for Open Water cert - Once certified with any agency, you can dive at any reputable shop globally
Course duration: 3–4 days for Open Water (theory, pool, ocean dives) Minimum age: 10 (Junior OW) or 15 (full OW) Health requirement: medical questionnaire — most conditions are fine, asthma/heart issues need doctor sign-off