Explanation

When commodity futures prices are in contango:

• The calendar spread is positive - This is correct because contango means longer-term futures prices exceed near-term futures prices
• The commodity forward curve is downward sloping - This describes backwardation, not contango. Contango has an upward-sloping forward curve
• The futures contract value tends to erode over time - While this can occur as futures converge to spot prices, it's not the defining characteristic of contango

Contango is defined by an upward-sloping forward curve where futures prices exceed spot prices, creating positive calendar spreads.