Ewart Oakeshott's typology of the medieval sword is based on blade morphology. It categorizes swords into 13 main types labelled X to XXII. Ewart Oakeshott introduced it in his The Archeology of Weapons: Arms and Armour from Prehistory to the Age of Chivalry 1960.
The system is a continuation of Jan Petersen's typology of the Viking sword, introduced in De Norske Vikingsverd ("The Norwegian Viking Swords", 1919), modified in 1927 by R. E. M. Wheeler into a typology of nine types labelled I to IX.
Oakeshott X describes the type of sword common in the late Viking age, remaining in use up to the 13th century. They feature broad and flat blades, with an average length of some 80 cm (2.6 feet) and with a fuller, generally very wide and shallow, running almost the entire length, but fading out shortly before the point. The point is typically rounded. The grip has the same average length as the earlier Viking swords (some 9.5 cm or 3.7 inches). The tang, usually very flat and broad, tapers sharply towards the pommel. The cross is generally of square section, about 18 to 20 cm long (7 to 7.8 inches), tapering towards the tips, in some rare cases slightly curved. It is narrower and longer than the typical Viking type, representing a transitional type to the knightly sword of the high Middle Ages. 10th-century Norsemen knew this type and called it gaddhjalt (spike hilt). The pommels usually take a Brazil-nut form, and sometimes also a disk-shape. 
In 1981, Oakeshott introduced the a subtype Xa, including swords with similar blades but a narrower fuller, originally classified under type XI. Many of the type X blades have inscribed the ULFBERHT mark.
Tapering point, in use ca. 1100–1175. Subtype XIa has a broader, shorter blade.
Typical of the high Middle Ages, these swords begin to show a tapering of the blade with a shortened fuller, resulting in improved thrusting characteristics while maintaining good cutting capabilities. A large number of medieval examples of this type survive. It certainly existed in the later 13th century, and perhaps considerably earlier, since the Schweizerisches Landesmuseum in Zurich possesses an example that has a Viking Age-type hilt, but clearly a type XII blade. The subtype XIIa (originally classified as XIIIa) consists of the longer, more massive greatswords that appear in the mid-13th century, probably designed to counter the improved mail armour of the time, and the predecessor of the later longswords. The earliest known depiction of a type XII sword in art forms part of the Archangel Michael statue in Bamberg Cathedral, dating to circa 1200. The Maciejowski Bible (circa 1245) depicts other examples.
This typifies the classical knightly sword that developed during the age of the Crusades. Typically, examples date to the second half of the 13th century. Type XIII swords feature as a defining characteristic a long, wide blade with parallel edges, ending in a rounded or spatulate tip. The blade cross section has the shape of a lens. The grips, longer than in the earlier types, typically some 15 cm (almost 6 inches), allow occasional two-handed use. The cross-guards are usually straight, and the pommels Brazil-nut or disk-shaped (Oakeshott pommel types D, E and I).
Subtype XIIIa features longer blades and grips. They correspond to the knightly greatswords, or Grans espées d'Allemagne, appearing frequently in 14th century German, but also in Spanish and English art. Early examples of the type appear in the 12th century, and it remained popular until the 15th century. Subtype XIIIb describes smaller single-handed swords of similar shape.
Very few examples of the parent type XIII exist, while more examples of the subtype XIIIa survive. A depiction of two-handed use appears in the Tenison psalter. Another depiction of the type appears in the Apocalypse of St. John manuscript of circa 1300.
Ewart Oakeshott describes swords of Type XIV classification as "...short, broad and sharply-pointed blade, tapering strongly from the hilt, of flat section (the point end of the blade may, in some examples, have a slight though perceptible mid-rib, with a fuller running about half, or a little over, of its length. This may be single and quite broad or multiple and narrow. The grip is generally short (average 3.75") though some as long as 4.5"; the tang is thick and parallel-sided, often with the fuller extending half-way up it. The pommel is always of "wheel" form, sometimes very wide and flat. The cross is generally rather long and curved (very rarely straight)."
Tapering blade with diamond cross-section and a sharp point. In use ca. 1300–1500. Type XVa have longer, narrower blades, for example the fencing swords of the school of Johannes Liechtenauer.
Blade length ca. 70-80cm. Subtype XVIa have a longer blade with a shorter fuller (usually running down 1/3 and rarely exceeding 1/2 of the blade). The grip is often extended to accommodate one and a half or two hands.
Long, tapering blade, hexagonal cross section, two-handed grip. Heavy swords, weighing more than 2 kg, used to pierce armour. In use ca. 1360–1420.
Tapering blades with broad base, short grip, diamond cross-section. The subtype XVIIIa have narrow blades with a longer grip. Subtype XVIIIb have a longer blade and long grip and were in use ca. 1450–1520. Subtype XVIIIc: broad blade of ca. 90 cm.
15th century swords for one-handed use, with broad flat blades, parallel edges, narrow fullers, ricasso.
14th to 15th century "hand and a half" swords, often with two fullers. Subtype XXa have narrower blades.
Cinquedea-like swords, late 15th century. Somewhat longer and less broad than the Cinquedas.
Broad flat blades, two short, narrow fullers, around 1500.
- Oakeshott institute
- Ewart Oakeshott: The Man and his Legacy (myArmoury.com article)
- myArmoury.com features:
- Spotlight: Oakeshott Type X Swords
- Spotlight: Oakeshott Type XI Swords
- Spotlight: Oakeshott Type XII Swords
- Spotlight: Oakeshott Type XIII Swords
- Spotlight: Oakeshott Type XIV Swords
- Spotlight: Oakeshott Type XV Swords
- Spotlight: Oakeshott Type XVI Swords
- Spotlight: Oakeshott Type XVII Swords
- Spotlight: Oakeshott Type XVIII Swords
- Spotlight: Oakeshott Type XIX Swords
- Spotlight: Oakeshott Type XX Swords
- Spotlight: Oakeshott Type XXI and XXII Swords