diff --git a/lib/ocaml/baseline/csv.ml b/lib/ocaml/baseline/csv.ml
new file mode 100644
index 00000000..56a023f3
--- /dev/null
+++ b/lib/ocaml/baseline/csv.ml
@@ -0,0 +1,12 @@
+let sum_second_col text =
+  let lines = String.split_on_char '\n' text in
+  List.fold_left (fun acc line ->
+    let fields = String.split_on_char ',' line in
+    if List.length fields >= 2 then
+      acc + int_of_string (List.nth fields 1)
+    else acc
+  ) 0 lines
+
+;;
+
+sum_second_col "a,1,extra\nb,2,extra\nc,3,extra\nd,4,extra"
diff --git a/lib/ocaml/baseline/expected.json b/lib/ocaml/baseline/expected.json
index fe38a370..343c9c3b 100644
--- a/lib/ocaml/baseline/expected.json
+++ b/lib/ocaml/baseline/expected.json
@@ -5,6 +5,7 @@
   "caesar.ml": 215,
   "calc.ml": 13,
   "closures.ml": 315,
+  "csv.ml": 10,
   "exception_handle.ml": 4,
   "expr_eval.ml": 16,
   "factorial.ml": 3628800,
diff --git a/plans/ocaml-on-sx.md b/plans/ocaml-on-sx.md
index d150efe9..29cfc0cf 100644
--- a/plans/ocaml-on-sx.md
+++ b/plans/ocaml-on-sx.md
@@ -407,6 +407,11 @@ _Newest first._
   binary search tree (`type 'a tree = Leaf | Node of 'a * 'a tree *
   'a tree`) with insert + in-order traversal. Tests parametric ADT,
   recursive match, List.append, List.fold_left.
+- 2026-05-09 Phase 5.1 — csv.ml baseline (split on '\n' then ',',
+  parse-int the second field, fold-left). Exercises char escapes
+  inside string literals, two-stage String.split_on_char, mixed
+  List.fold_left + int_of_string + List.nth. Sums column 2 of a
+  4-row inline CSV → 1+2+3+4 = 10. 23 baseline programs total.
 - 2026-05-09 Phase 4 — polymorphic variants confirmation (+3 tests,
   506 total). The tokenizer was already classifying `` `Tag `` as a
   ctor identical to a nominal one, but it had never been exercised by