diff --git a/planning/grpc/server/src/chronicles.rs b/planning/grpc/server/src/chronicles.rs
index 604c4925..991329bb 100644
--- a/planning/grpc/server/src/chronicles.rs
+++ b/planning/grpc/server/src/chronicles.rs
@@ -895,12 +895,47 @@ impl<'a> ChronicleFactory<'a> {
     }
 
     fn set_cost(&mut self, cost: &Expression) -> Result<(), Error> {
-        ensure!(kind(cost)? == ExpressionKind::Constant);
-        ensure!(cost.r#type == "up:integer");
-        let cost = match cost.atom.as_ref().unwrap().content.as_ref().unwrap() {
-            Content::Int(i) => *i as IntCst,
-            _ => bail!("Unexpected cost type."),
+        let tpe = from_upf_type(cost.r#type.as_ref(), &self.context.model.get_symbol_table().types)
+            .with_context(|| format!("Unknown argument type: {0}", cost.r#type))?;
+        ensure!(tpe.is_numeric());
+
+        let cost = match kind(cost)? {
+            ExpressionKind::Constant => {
+                ensure!(cost.r#type == "up:integer");
+                Cost::Fixed(match cost.atom.as_ref().unwrap().content.as_ref().unwrap() {
+                    Content::Int(i) => *i as IntCst,
+                    _ => bail!("Unexpected cost type."),
+                })
+            }
+            ExpressionKind::Parameter => {
+                let name = match cost.atom.as_ref().unwrap().content.as_ref().unwrap() {
+                    Content::Symbol(s) => s.clone(),
+                    _ => bail!("Unexpected cost parameter name type."),
+                };
+                let var = self
+                    .env
+                    .parameters
+                    .get(&name)
+                    .with_context(|| format!("Unknown parameter: {name}"))?;
+                match var {
+                    Variable::Int(var) => Cost::Variable(*var),
+                    _ => bail!("Cost parameter must be an integer variable."),
+                }
+            }
+            _ => bail!("Unsupported cost expression: {cost:?}"),
         };
+
+        match cost {
+            Cost::Fixed(cost) => ensure!(cost >= 0, "Cost must be a non-negative integer ({cost})"),
+            Cost::Variable(..) => match tpe {
+                Type::Int { lb, .. } => ensure!(
+                    lb >= 0,
+                    "Cost variable must be a non-negative integer (lower bound = {lb})"
+                ),
+                _ => bail!("Cost variable must be an integer variable."),
+            },
+        };
+
         self.chronicle.cost = Some(cost);
         Ok(())
     }
diff --git a/planning/planners/src/encode.rs b/planning/planners/src/encode.rs
index f3a4f581..e4d5ce4d 100644
--- a/planning/planners/src/encode.rs
+++ b/planning/planners/src/encode.rs
@@ -428,8 +428,13 @@ pub fn add_metric(pb: &FiniteProblem, model: &mut Model, metric: Metric) -> IAto
             // retrieve the presence and cost of each chronicle
             let mut costs = Vec::with_capacity(8);
             for (ch_id, ch) in pb.chronicles.iter().enumerate() {
-                if let Some(cost) = ch.chronicle.cost {
-                    assert!(cost >= 0, "A chronicle has a negative cost");
+                if let Some(cost) = &ch.chronicle.cost {
+                    match cost {
+                        Cost::Fixed(c) => assert!(*c >= 0, "A chronicle has a negative cost"),
+                        Cost::Variable(v) => {
+                            assert!(model.domain_of(*v).0 >= 0, "A chronicle could have a negative cost")
+                        }
+                    };
                     costs.push((ch_id, ch.chronicle.presence, cost));
                 }
             }
@@ -438,8 +443,12 @@ pub fn add_metric(pb: &FiniteProblem, model: &mut Model, metric: Metric) -> IAto
             let action_costs: Vec<LinearTerm> = costs
                 .iter()
                 .map(|&(ch_id, p, cost)| {
+                    let bounds = match cost {
+                        Cost::Fixed(c) => (*c, *c),
+                        Cost::Variable(v) => model.domain_of(*v),
+                    };
                     model
-                        .new_optional_ivar(cost, cost, p, Container::Instance(ch_id).var(VarType::Cost))
+                        .new_optional_ivar(bounds.0, bounds.1, p, Container::Instance(ch_id).var(VarType::Cost))
                         .or_zero(p)
                 })
                 .collect();
diff --git a/planning/planning/src/chronicles/concrete.rs b/planning/planning/src/chronicles/concrete.rs
index a23b79b3..857c51c6 100644
--- a/planning/planning/src/chronicles/concrete.rs
+++ b/planning/planning/src/chronicles/concrete.rs
@@ -280,6 +280,24 @@ impl Substitute for StateVar {
     }
 }
 
+/// The cost of a chronicle
+#[derive(Clone, Debug)]
+pub enum Cost {
+    /// The cost is a fixed integer value
+    Fixed(IntCst),
+    /// The cost is a chronicle's variable
+    Variable(IVar),
+}
+
+impl Substitute for Cost {
+    fn substitute(&self, s: &impl Substitution) -> Self {
+        match self {
+            Cost::Fixed(x) => Cost::Fixed(*x),
+            Cost::Variable(x) => Cost::Variable(s.sub_ivar(*x)),
+        }
+    }
+}
+
 /// Represents an effect on a state variable.
 /// The effect has a first transition phase `]transition_start, transition_end[` during which the
 /// value of the state variable is unknown.
@@ -493,7 +511,7 @@ pub struct Chronicle {
     /// expression on the start/end timepoint of these subtasks.
     pub subtasks: Vec<SubTask>,
     /// Cost of this chronicle. If left empty, it is interpreted as 0.
-    pub cost: Option<IntCst>,
+    pub cost: Option<Cost>,
 }
 
 struct VarSet(HashSet<VarRef>);
@@ -625,7 +643,7 @@ impl Substitute for Chronicle {
             effects: self.effects.iter().map(|e| e.substitute(s)).collect(),
             constraints: self.constraints.iter().map(|c| c.substitute(s)).collect(),
             subtasks: self.subtasks.iter().map(|c| c.substitute(s)).collect(),
-            cost: self.cost,
+            cost: self.cost.as_ref().map(|c| c.substitute(s)),
         }
     }
 }
diff --git a/planning/planning/src/chronicles/printer.rs b/planning/planning/src/chronicles/printer.rs
index df7e5ec5..c5c25e17 100644
--- a/planning/planning/src/chronicles/printer.rs
+++ b/planning/planning/src/chronicles/printer.rs
@@ -99,8 +99,8 @@ impl<'a> Printer<'a> {
             println!()
         }
 
-        if let Some(cost) = ch.cost {
-            println!("  cost: {cost}")
+        if let Some(cost) = &ch.cost {
+            println!("  cost: {cost:?}")
         }
 
         println!()
diff --git a/planning/planning/src/parsing/mod.rs b/planning/planning/src/parsing/mod.rs
index 84f2290d..e5cf8b8b 100644
--- a/planning/planning/src/parsing/mod.rs
+++ b/planning/planning/src/parsing/mod.rs
@@ -393,7 +393,7 @@ fn read_chronicle_template(
     // TODO: here the cost is simply 1 for any primitive action
     let cost = match pddl.kind() {
         ChronicleKind::Problem | ChronicleKind::Method => None,
-        ChronicleKind::Action | ChronicleKind::DurativeAction => Some(1),
+        ChronicleKind::Action | ChronicleKind::DurativeAction => Some(Cost::Fixed(1)),
     };
 
     let mut ch = Chronicle {
diff --git a/planning/unified/plugin/up_aries_tests/__init__.py b/planning/unified/plugin/up_aries_tests/__init__.py
index 99c940cd..bb6f2e13 100644
--- a/planning/unified/plugin/up_aries_tests/__init__.py
+++ b/planning/unified/plugin/up_aries_tests/__init__.py
@@ -42,7 +42,7 @@ def test_action_costs():
     a = InstantaneousAction("a")
     a.add_precondition(Not(pa))
     a.add_effect(pa, True)
-    b = InstantaneousAction("b", k=IntType())
+    b = InstantaneousAction("b", k=IntType(lower_bound=0))
     b.add_precondition(Not(pb))
     b.add_effect(pb, True)
     costs = {a: 10, b: b.k}